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Diffraction

(adapted from Giancoli Physics)

Waves spread as they travel. When waves encounter an obstacle, they bend around it and pass into the region behind it. This phenomenon is called diffraction.
Wave diffraction
The amount of diffraction depends on the λ (wavelength) of the wave and on the size of the obstacle:

Water waves diffraction

(a) λ is much larger than the object. Wave bends around object almost as if it is not there.

(b) and (c) the λ is shorter than the size of the object. There’s more of a “shadow” region behind the obstacle where we might not expect the waves to penetrate — but they do, at least a little.

(d) the obstacle is the same as in part (c) but the λ is longer. More diffraction around object.

Rule: Only when λ is smaller than the size of the object will there be a shadow region.

Water waves diffracting around an island

wave-diffraction-around-island-by-marcelzijlema-a

And then the next step

wave-diffraction-around-island-by-marcelzijlema-b

Sound waves can diffract in unusual and unexpected ways. See our article on anomalous sounds

Even light itself can diffract!  See our article on light’s wave nature.

Fresnel diffraction

French scientist, Augustin-Jean Fresnel,

Discovering Fresnel diffraction: The Greatest Mistake In The History Of Physics

Example – diffraction in Boston Harbor

spectacle Island Boston Harbor

from bostonfoodandwhine.com

As part of the Central Artery/Tunnel project – the Big Dig – Applied Coastal Research and Engineering did research on wave diffraction in Boston Harbor, around Spectacle Island.

…A detailed beach nourishment design was developed for the southern shoreline of Spectacle Island, which is located within Boston Harbor…  The propagation of waves from Massachusetts Bay into Boston Harbor was modeled using the refraction/diffraction model REF/DIF1. This model predicts the transformation of waves in areas where bathymetry is irregular and where diffraction is important, such as at Spectacle Island. The resulting wave heights, periods, and directions were used as input to both longshore and cross-shore sediment transport models. These models were employed to simulate the performance of several different beach fill designs…

Beach Nourishment Design for Spectacle Island

Spectacle Island Boston Harbor Diffraction

Boston Harbor Islands map

This map is from mass.gov/eea/images/dcr

Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

HS-PS4-1. Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling within various media. Recognize that electromagnetic waves can travel through empty space (without a medium) as compared to mechanical waves that require a medium

HS-PS4-3. Evaluate the claims, evidence, and reasoning behind the idea that electromagnetic radiation can be described either by a wave model or a particle model, and that for some situations one model is more useful than the other. [Emphasis is on how the experimental evidence supports the claim and how a theory is generally modified in light of new evidence. Examples of a phenomenon could include resonance, interference, diffraction, and photoelectric effect.]

Anomalous sounds

Here’s an actual news story: “Loud booms heard across Southern New Hampshire: Source of the noise still unclear.”

Nashua police say they don’t know what caused several loud “booms” Saturday afternoon that were heard across Southern New Hampshire. Many reports came from Nashua and surrounding towns, but the sounds were reported as far north as Manchester and as far south as Westford, Massachusetts. Some who heard it in Nashua said they felt their houses shake. Police and fire departments said they have not been alerted to any incidents related to the noise in the area. The cause is still unclear.
– WMUR 9 News. (An ABC affiliated TV station) 2/10/18

How is it possible that such loud, possibly building shaking sounds could be heard in some parts of this town – yet in other parts of the city other residents reported no sound? Also, in a town next door no reports have yet surfaced of anyone hearing them – yet in a town after that, some residents also reported these booming sound.

The answer? It’s complicated, but basically:

(a) there are a wide variety of ways that sounds are produced – including some bizarre ways that most people have never heard of

(b) Sound waves don’t always move in a straight path like many people imagine; changing temperature/density of the air can cause sound waves to bend and diffract, so:

(b1) sound can sometimes travel much further distances than one would expect

(b2) sound can come from a location very different from what “seems obvious” just by listening

(b3) local wind can mask sound, so the same loud sound might be heard in one neighborhood, yet be undetectable by people just a mile away.

Basic idea

Sound doesn’t move in a straight line: It spreads out radially, and then – because of a phenomenon known as diffraction – it can even bend around obstacles.

Diffraction of sound Hyperphysics

Source: Hyperphysics, Diffraction of sound, http://hyperphysics.phy-astr.gsu.edu/

“If the air above the earth is warmer than that at the surface, sound will be bent back downward toward the surface by refraction.” – Hyperphysics

sound refraction Hyperphysics 2

Normally, only sound initially directed toward the listener can be heard, but refraction can bend sound downward – effectively amplifying the sound.

This can occur over cool lakes.

sound refraction Hyperphysics 3

Sounds also can bounce off of objects, and come to our ears from a direction different than the original source.

sound-reflection

ABD Engineering writes:

…wind alters sound propagation by the mechanism of refraction; that is, wind bends sound waves. Wind nearer to the ground moves more slowly than wind at higher altitudes, due to surface characteristics such as hills, trees, and man-made structures that interfere with the wind.

This wind gradient, with faster wind at higher elevation and slower wind at lower elevation causes sound waves to bend downward when they are traveling to a location downwind of the source and to bend upward when traveling toward a location upwind of the source.

Waves bending downward means that a listener standing downwind of the source will hear louder noise levels than the listener standing upwind of the source.

Temperature gradients in the atmosphere. On a typical sunny afternoon, air is warmest near the ground and temperature decreases at higher altitudes. This temperature gradient causes sound waves to refract upward, away from the ground and results in lower noise levels being heard at the listener’s position.

In the evening, this temperature gradient will reverse, resulting in cooler temperatures near the ground. This condition, often referred to is a temperature inversion will cause sound to bend downward toward the ground and results in louder noise levels at the listener position.

How Weather Affects an Outdoor Noise Study by ABD Engineering and Design

Cheung Kai-chung, from Physics World (Hong Kong), (Translation by Janny Leung) offers this explanation

Sound wave will be refracted to the ground when traveling with the wind.

Sound waves refracted 1

Sound wave will be refracted upwards when traveling against the wind.

sound waves refracted 2

Source:   Why can a distant sound be heard easier when it travels with the wind? Why does it become weaker if it travels against the wind?

Can wind mask even loud sounds?

A discussion to consider, from Physics forums, includes this phenomenon: “Yes. I have a freeway about 10 blocks South of my house. I can hear the traffic very clearly with no wind, or a South wind. If there is even a slight North wind, the traffic noise becomes almost inaudible. If there is a brisk North wind (over 15 MPH), the sound is completely gone.”

https://www.physicsforums.com/threads/does-wind-affect-how-far-sound-can-travel.149392/

Sound refraction due to cold air:

Also this “…if the air close to the ground is colder than the air above it then sound waves traveling upwards will be bent downwards. This is called Refraction. These refracted sound waves can act to amplify the sound to someone standing far away.”

http://sciencewows.ie/blog/does-sound-travel-faster-in-warm-or-cold-air/

Sound seems amplified when traveling over water.

In School-for-Champions we read

“If you are sitting in a boat, a sound coming from the shore will seem louder than the same sound heard by a person on land. Sound seems to be amplified when it travels over water. The reason is that the water cools the air above its surface, which then slows down the sound waves near the surface. This causes refraction or bending of the sound wave, such that more sound reaches the boat passenger. Sound waves skimming the surface of the water can add to the amplification effect, if the water is calm.”

sound_amplified_over_water_refraction

See their full lesson here School-for-champions.com: Sound_amplified_over_water

Can snow on the ground affect sound?

“When the ground has a thick layer of fresh, fluffy snow, sound waves are readily absorbed at the surface of the snow. However, the snow surface can become smooth and hard as it ages or if there have been strong winds. Then the snow surface will actually help reflect sound waves. Sounds seem clearer and travel farther under these circumstances.” – Colorado State Climatologist Nolan Doesken

Related topic: The Hum is a phenomenon, or collection of phenomena, involving widespread reports of a persistent and invasive low-frequency humming, rumbling, or droning noise not audible to all people.

“Hums” have been widely reported by national media in the UK and the United States. The Hum is sometimes prefixed with the name of a locality where the problem has been particularly publicized: e.g., the “Bristol Hum” or the “Taos Hum”. It is unclear whether it is a single phenomenon; different causes have been attributed. ”

Human reactions to infrasound –

https://en.wikipedia.org/wiki/Infrasound#Human_reactions

Skyquakes or mystery booms are unexplained reports of a phenomenon that sounds like a cannon or a sonic boom coming from the sky. They have been heard in several locations around the world. –

https://en.wikipedia.org/wiki/Skyquake

The microwave auditory effect, also known as the microwave hearing effect or the Frey effect, consists of audible clicks (or, with speech modulation, spoken words[citation needed]) induced by pulsed/modulated microwave frequencies. The clicks are generated directly inside the human head without the need of any receiving electronic device. The effect was first reported by persons working in the vicinity of radar transponders during World War II. (Wikipedia)

References

Our first article.

How Weather Affects an Outdoor Noise Study by ABD Engineering and Design

This following discussion has helpful images.

Why can a distant sound be heard easier when it travels with the wind? Why does it become weaker if it travels against the wind?

A discussion to consider, from Physics forums, includes this phenomenon:
“Yes. I have a freeway about 10 blocks South of my house. I can hear the traffic very clearly with no wind, or a South wind. If there is even a slight North wind, the traffic noise becomes almost inaudible. If there is a brisk North wind (over 15 MPH), the sound is completely gone.”

https://www.physicsforums.com/threads/does-wind-affect-how-far-sound-can-travel.149392/

Also this “…if the air close to the ground is colder than the air above it then sound waves traveling upwards will be bent downwards. This is called Refraction. These refracted sound waves can act to amplify the sound to someone standing far away.”

http://sciencewows.ie/blog/does-sound-travel-faster-in-warm-or-cold-air/

Sound seems amplified when traveling over water

https://www.school-for-champions.com/science/sound_amplified_over_water.htm#.WoBbQ5M-fVo

Diffraction of sound waves

https://katrinasiron21.wordpress.com/properties-of-sound-waves/diffraction-of-sound-waves/

Temperature inversion and sound waves

http://kxan.com/blog/2015/02/13/why-does-sound-carry-farther-on-cold-calm-mornings/

Also look into: Humans hearing infra sound waves

“Colorado State Climatologist Nolan Doesken says: “When the ground has a thick layer of fresh, fluffy snow, sound waves are readily absorbed at the surface of the snow. However, the snow surface can become smooth and hard as it ages or if there have been strong winds. Then the snow surface will actually help reflect sound waves. Sounds seem clearer and travel farther under these circumstances.””

Related topic: The Hum is a phenomenon, or collection of phenomena, involving widespread reports of a persistent and invasive low-frequency humming,rumbling, or droning noise not audible to all people. Hums have been widely reported by national media in the UK and the United States. The Hum is sometimes prefixed with the name of a locality where the problem has been particularly publicized: e.g., the “Bristol Hum” or the “Taos Hum”. It is unclear whether it is a single phenomenon; different causes have been attributed. ”

Human reactions to infrasound – https://en.wikipedia.org/wiki/Infrasound#Human_reactions

Skyquakes or mystery booms are unexplained reports of a phenomenon that sounds like a cannon or a sonic boom coming from the sky. They have been heard in several locations around the world. – https://en.wikipedia.org/wiki/Skyquake

Learning Standards

Skeptical analysis of unexplained phenomenon.

The Massachusetts STEM Curriculum Framework addresses “Understandings about the Nature of Science”

Scientific inquiry is characterized by a common set of values that include: logical thinking, precision, open-mindedness, objectivity, skepticism, replicability of results, and honest and ethical reporting of findings.

Science disciplines share common rules of evidence used to evaluate explanations about natural systems. Science includes the process of coordinating patterns of evidence with current theory.

Most scientific knowledge is quite durable but is, in principle, subject to change based on new evidence and/or reinterpretation of existing evidence.

The “College Board Standards for College Success: Science” addresses these same skeptical inquiry methods in Standard SP.1: Scientific Questions and Predictions. Asking scientific questions that can be tested empirically and structuring these questions in the form of testable predictions.

Students recognize, formulate, justify and revise scientific questions that can be addressed by science in order to construct explanations.

Students make and justify predictions concerning natural phenomena. Predictions and justifications are based on observations of the world, on knowledge of the discipline and on empirical evidence.

Students determine which data from a specific investigation can be used as evidence to address a scientific question or to support a prediction or an explanation, and distinguish credible data from noncredible data in terms of quality.

Students construct explanations that are based on observations and measurements of the world, on empirical evidence and on reasoning grounded in the theories, principles and concepts of the discipline.

The “Benchmarks for Science Literacy” (AAAS) addresses these same skeptical inquiry methods:

In science, a new theory rarely gains widespread acceptance until its advocates can show that it is borne out by the evidence, is logically consistent with other principles that are not in question, explains more than its rival theories, and has the potential to lead to new knowledge. 12A/H3** (SFAA)

Scientists value evidence that can be verified, hypotheses that can be tested, and theories that can be used to make predictions. 12A/H4** (SFAA)

Curiosity motivates scientists to ask questions about the world around them and seek answers to those questions. Being open to new ideas motivates scientists to consider ideas that they had not previously considered. Skepticism motivates scientists to question and test their own ideas and those that others propose. 12A/H5*

SAT subject test in Physics: Waves and optics

• General wave properties, such as wave speed, frequency, wavelength, superposition, standing wave diffraction, and Doppler effect

 

Binnacle

Our school is right by Boston Harbor – learning about the sea is second nature to many of our staff. So we love to tie maritime history and science into our curriculum.

Binnacle maritime

Photo by RK

As you enter our school, you pass by a binnacle – what was it used for?

A binnacle is a waist-high case, found on the deck of a ship, that holds the compass.

It is mounted in gimbals to keep it level while the ship pitched and rolled.

It also has a mechanism to compensate for errors in detecting the Earth’s magnetic field.

Every ship’s captain would use one, for navigating in and out of Boston Harbor, and around the world.

 

Here we see Boston Harbor – now let’s get in to how the binnacle works!

Boston Harbor Islands map

This map is from mass.gov/eea/images/dcr

 

Why did we need to develop the binnacle?

Excerpted from Magnetic Deviation: Comprehension, Compensation and Computation by Ron Doerfler  

Today, radio navigational systems such as LORAN and GPS, and inertial navigation systems with ring and fiber-optic gyros, gyrocompasses and the like have reduced the use of a ship’s compass to worst-case scenarios. But this triumph of mathematics and physics over the mysteries of magnetic deviation, entered into at a time when magnetic forces were barely understood and set against the backdrop of hundreds of shipwrecks and thousands of lost lives, is an enriching chapter in the history of science.

The Sources of Compass Error

Ron Doerfler writes:

Compasses on ships fail to point to true (geographic) north due to two factors:

Magnetic variation (or magnetic declination) – the angle between magnetic north and geographic north due to the local direction of the Earth’s magnetic field, and

Magnetic deviation – the angle between the compass needle and magnetic north due to the presence of iron within the ship itself.

The algebraic sum of the magnetic variation and the magnetic deviation is known as the compass error. It is a very important thing to know.

Magnetic Variation

Magnetic variation has been known from voyages since the early 1400s at least. Certainly Columbus was distressed as he crossed the Atlantic to find that magnetic north and true north (from celestial sightings) drifted significantly…

We now know that the locations of the Earth’s magnetic poles are not coincident with the geographic poles—not even close, really—and they are always wandering around.

magnetic north pole deviation

Image from commons.wikimedia.org, Magnetic_North_Pole_Positions. Red circles mark magnetic north pole positions as determined by direct observation, blue circles mark positions modelled using the GUFM model (1590–1980) and the IGRF model (1980–2010) in 2 year increments.

 

What’s the difference between where a compass needle points (magnetic north) and the geographic north pole? This is called the declination  It’s smallest near the equator, but generally gets large as one moves towards the poles.

On this map, the green arrows – the direction from the compass – point towards the magnetic north. The red arrows point towards the geographical north pole.

Notice how the left location (in Pacific ocean) shows the compass point a bit east of where we’d hope it would point; in the right location (in Atlantic Ocean) it shows the compass point a bit west of where we’d hope it points.

There’s also a special line where the magnetic north and geographic north point in the same direction.

Magnetic Declination

Image from Drillingformulas.com by Rachain J i

 

Here we can see how many degrees of deviation there are – the # of degrees between where the compass points, and where the north pole is. But – wait for it – the image is changing? The magnetic fields are significantly changing every year!

Estimated declination contours by year

from USGS.gov, faqs, what is declination

 

Magnetic Deviation

Ron Doerfler writes

There is an additional effect on the compass needle that took much longer to appreciate and even longer to understand. This magnetic deviation is due to the iron in a ship…

The first notice in print of this effect was by Joao de Castro of Portugal in 1538, in which he identified “the proximity of artillery pieces, anchors and other iron” as the source.

As better compass designs appeared, a difference in compass readings with their placement on the same ship became more apparent. Captains John Smith and James Cook warned about iron nails in the compass box or iron in steerage, and on Cook’s second circumnavigation William Wales found that changes in the ship’s course changed their measurements of magnetic variation by as much as 7°.

Here we see a modern naval vessel, with it’s own magnetic field. As a metal ship moves through Earth’s magnetic field, an electric current is produced within all that metal – and that current produces it’s own magnetic field. This field can affect the ship’s compass. That’s why a binnacle is designed to be adjustable, to compensate for this field. – RK

Degaussing magnetic field ship

image from slideplayer.com/slide/1632522/

 

Ron Doerfler writes

Captain Matthew Flinders (1774-1815) spent years in the very early 1800s on voyages to investigate these effects…. [he] eventually discovered that an iron bar placed vertically near the compass helped overcome the magnetic deviation. This Flinder’s bar is still used today in ships’ binnacles.

 

Apps & Interactives

NOAA Historical Magnetic Declination

Activities

Hands-on Activity: Nautical Navigation. Teachengineering.org

https://oceanservice.noaa.gov/education/lessons/plot_course.html

https://asa.com/certifications/asa-105-coastal-navigation/

 

Educational opportunities and museums

http://www.capecodmaritimemuseum.org/education/

https://timeandnavigation.si.edu/navigating-at-sea/longitude-problem/solving-longitude-problem/chronometer

http://abycinc.org/?page=standards

Important components

Quadrantal spheres (spherical quadrantal correctors)

Hood, over the compass bowl

flinders bar (vertical, soft iron corrector)

Learning Standards

Ocean Literacy Scope and Sequence for Grades K-12
6. The ocean and humans are inextricably interconnected: From the ocean we get foods, medicines, and mineral and energy resources. In addition, it provides jobs, supports our nation’s economy, serves as a highway for transportation of goods and people, and plays a role in national security.

Massachusetts 2016 Science and Technology/Engineering (STE) Standards
7.MS-PS2-5. Use scientific evidence to argue that fields exist between objects with mass, between magnetic objects, and between electrically charged objects that exert force on each other even though the objects are not in contact.

HS-PS2-1. Analyze data to support the claim that Newton’s second law of motion is a mathematical model describing change in motion (the acceleration) of objects when acted on by a net force….{forces can include magnetic forces}

HS-PS3-5. Develop and use a model of magnetic or electric fields to illustrate the forces and changes in energy between two magnetically or electrically charged objects changing relative position in a magnetic or electric field, respectively.

History standards

National Standards for History Basic Edition, 1996
5-12 Identify major technological developments in shipbuilding, navigation, and naval warfare and trace the cultural origins of various innovations.

Massachusetts History and Social Science Curriculum Framework
The Political, Intellectual and Economic Growth of the Colonies. Explain the importance of maritime commerce in the development of the economy of colonial Massachusetts, using historical societies and museums as needed.

National Curriculum Standards for Social Studies: A Framework for Teaching, Learning, and Assessment, National Council for the Social Studies, 2010.

 

PSAT Science questions

Olympics

About the PSAT

This is designed to measure the ability to understand and process elements of reading, writing, and mathematics…. The College Board now also offers two PSAT variations: the PSAT 10 for sophmores, and the PSAT 8/9 for freshmen and eighth graders. These variations generate score reports that measure students’ college readiness and skillsets. (the PSAT 8/9 is shorter and less complex). Read more about the PSAT variations.   It has four sections:

  • The Reading Test – 60 minutes, 47 questions
  • The Writing and Language Test – 35 minutes, 44 questions
  • Math Test, No Calculator Portion – 25 minutes, 17 questions
  • Math Test, Calculator Portion – 45 minutes, 31 questions

The PSAT/NMSQT and PSAT 10 both have a total testing time of 2 hours and 45 minutes.

= from testmasters.net

======

from the Kaplan website kaptest.com/study/psat/psat-reading-science-passages/

The PSAT Reading Test will contain either two single Science passages or one single Science passage and one set of paired Science passages. Science passages differ from other passage types because:

  • They often contain a lot of jargon and technical terms.
  • They can utilize unfamiliar terms and concepts.

While Science passages can be tricky due to unfamiliar language, you will never need to employ knowledge outside of the passage when answering questions. Use the following strategy when approaching Science passages on the PSAT:

  •  LOCATE THE CENTRAL IDEA IN THE FIRST PARAGRAPH.
  •  NOTE HOW EACH PARAGRAPH RELATES TO THE CENTRAL IDEA.

    Does the paragraph…Explain? Support? Refute? Summarize?

  •  DON’T BE DISTRACTED BY JARGON OR TECHNICAL TERMS.

    Unfamiliar terms will generally be defined within the passage or in a footnote.

Let’s look at the following example of an abbreviated Science passage and question set. After the mapped passage, the left column contains questions similar to those you’ll see on the PSAT Reading Test on Test Day. The column on the right features the strategic thinking a test expert employs when approaching the passage and questions presented. Note how a test expert can quickly condense the entire passage into a few words and use his or her Passage Map to ask questions that build a prediction for the correct answer.

REMINDER

When you encounter more than one theory or idea, paraphrase each in as few words as possible in your Passage Map.

Sample PSAT Reading Practice Question: Science

Questions 1-2 are based on the following passage. This passage is adapted from an essay about the characteristics of lunar eclipses.

Many people are aware of the beauty of a solar eclipse, but are surprised to learn that lunar eclipses are often just as spectacular and are both more common and easier to observe. The filtering and refraction of light from the Earth’s atmosphere during a lunar eclipse creates stunning color effects that range from dark brown to red, orange, and yellow. Each of these light shows is unique since they are the result of the amount of dust and cloud cover in the Earth’s atmosphere at the time of the eclipse.

While total solar eclipses last only for a few minutes and can be seen only in a small area of a few kilo- meters, total lunar eclipses can last for several hours and can be seen over much of the planet. In fact, the beauty and stability of lunar eclipses make them a favorite of both amateur and professional photographers. Lunar eclipses generally occur two to three times a year and are possible only when the Moon is in its full phase. When we see the Moon, we are actually seeing sunlight reflected off the surface of the Moon. When the Earth is positioned in between the Moon and the Sun, however, the Earth’s shadow falls on the Moon and a lunar eclipse occurs. To better understand this process, it’s helpful to imagine the Earth’s shadow on the Moon as a pair of nested cones, with the Earth at the apex of the cones, and the Moon at their bases. The outer, more diffuse cone of shadow is called the penumbral shadow, while the inner, darker cone is the umbral shadow.

1. According to the passage, the colors of a lunar eclipse are the result of

(A) the penumbral shadow.

(B) the stability of lunar eclipses.

(C) filtering and refraction of light.

(D) the sunlight reflected off the moon.

2. In lines 26-27, the phrase “pair of nested cones” serves to

(A) offer support for a previous statement.

(B) describe the diffraction of light through the atmosphere.

(C) explain why lunar eclipses are favorites of photographers.

(D) provide a concrete example to help readers visualize a phenomenon.

Explanations of answers:

For practice question #1, use the Passage Map to find where the author mentions color. Because the author mentions both “filtering” and “dust,” you know that the right answer will include those. Choice (C) mentions “filtering” and is, therefore, correct.

For practice question #2, ask “Why did the author choose those words—what are they doing?” Could you picture how an eclipse worked? Predict that the phrase helps the reader understand the concept. Choice (D) matches exactly.

================

from 2015 Practice Test #1, Preliminary SAT/National Merit Scholarship Qualifying Test

Questions 20-28 are based on the following passage and supplementary material.
This passage is adapted from Tina Hesman Saey, “Lessons from the Torpid.” ©2012 by Society for Science & the Public.

Understanding how hibernators, including ground squirrels, marmots and bears, survive their long winter’s naps may one day offer solutions for problems such as heart disease, osteoporosis and muscular dystrophy. Nearly everything about the way an animal’s body
works changes when it hibernates, and preparations start weeks or months in advance. The first order of business is to fatten up.

“Fat is where it’s at for a hibernator,” says Matthew Andrews, a molecular biologist at the
University of Minnesota Duluth who studies 13-lined ground squirrels. “You bring your own lunch with you.” Packing lunch is necessary because the animals go on the world’s strictest diet during the winter, surviving entirely off their white fat. “They have their last supper in October; they don’t eat again until March,” Andrews says.

Bigger fat stores mean a greater chance of surviving until spring. “If they go in really chunky, nice and roly-poly, that’s going to be a good hibernator,” he says. Bears also watch their waistlines expand in the months before settling in for the season. The brown
bears cardiologist Ole Fröbert studies pack on the pounds by chowing down on up to 40 kilograms of blueberries a day. Such gluttony among humans could have severe consequences: Obesity is associated with a greater risk of heart attack and diabetes, among other ailments.

To see how fattening up affects Scandinavian brown bears, Fröbert and his colleagues
ventured into the wilds of Sweden following signals given off by radio transmitters or GPS devices on tagged bears.

Bears can be dangerous close-up. Even hibernating bears can rouse to action quickly, so
scientists tracking down bears in the winter use darts to tranquilize the animals from a distance. Scientists studying the bears in the summer tranquilize them from a helicopter.

Once a bear is under the tranquilizer’s influence (which takes about five minutes), the scientists have 60 minutes max to get the animal from its den, weigh and measure it, draw blood samples and do minor surgeries to collect fat and other tissues. The bear is returned to its den by minute 61.

Precious materials collected during this high-pressure encounter need to be analyzed within 24 hours, so the researchers often test for levels of cholesterol or certain proteins in the blood while working in the snow or at a nearby research station.  A pilot sometimes flies samples from field sites to a lab in Denmark in order to meet the deadline, Fröbert says. Samples such as bones and arteries that can’t be collected from live bears come from bears killed by hunters during the legal hunting season.

Recent analyses revealed that Scandinavian brown bears spend the summer with plasma cholesterol levels considered high for humans; those values then increase substantially for hibernation, Fröbert and his colleagues reported. These “very, very fat” bears with high cholesterol also get zero exercise during hibernation. Lolling about in the den pinches off blood vessels, contributing to sluggish circulation.

“That cocktail would not be advisable in humans,” Fröbert says. It’s a recipe for hardened arteries, putting people at risk for heart attacks and strokes. Even healthy young adult humans can develop fatty streaks in their arteries that make the blood
vessels less flexible, but the bears don’t build up such artery-hardening streaks. “Our bears, they had nothing,” Fröbert says. It’s not yet clear how the bears keep their arteries flexible, but Fröbert hopes to find some protective molecule that could stave off hardened arteries in humans as well.

Graph Plasma cholesterol

20. The passage is written from the perspective of someone who is
A) actively involved in conducting hibernator research.
B) a participant in a recent debate in the field of cardiology.
C) knowledgeable about advances in hibernator research.
D) an advocate for wildlife preservation.

21. It is reasonable to conclude that the main goal of the scientists conducting the research described in the passage is to
A) learn how the hibernation patterns of bears and squirrels differ.
B) determine the role that fat plays in hibernation.
C) illustrate the important health benefits of exercise for humans.
D) explore possible ways to prevent human diseases.

22. Which choice provides the best evidence for the answer to the previous question?
A) Lines 1-5 (“Understanding… dystrophy”)
B) Lines 10-13 (“Fat… squirrels”)
C) Lines 31-35 (“To… bears”)
D) Lines 42-46 (“Once… tissues”)

23. What main effect do the quotations by Andrews in lines 10-18 have on the tone of the passage?
A) They create a bleak tone, focusing on the difficulties hibernators face during the winter.
B) They create a conversational tone, relating scientific information in everyday language.
C) They create an ominous tone, foreshadowing the dire results of Andrews’s research.
D) They create an absurd tone, using images of animals acting as if they were human.

24. As used in line 19, “stores” most nearly means
A) preservatives.
B) reserves.
C) stacks.
D) shelters.

25 Based on the passage, what is Fröbert’s hypothesis regarding why bears’ arteries do not harden during hibernation?
A) The bears’ increased plasma cholesterol causes the arteries to be more flexible.
B) Sluggish circulation pinches off the blood vessels rather than hardening the arteries.
C) Bears exercise in short, infrequent bursts during hibernation, which staves off hardened arteries.
D) Bears possess a molecule that protects against hardened arteries.

26 Which choice provides the best evidence for the
answer to the previous question?
A) Lines 19-20 (“Bigger… spring”)
B) Lines 24-27 (“The brown… day”)
C) Lines 69-72 (“Even… streaks”)
D) Lines 73-76 (“It’s… well”)

27 What information discussed in paragraph 10 (lines 58-68) is represented by the graph?
A) The information in lines 58-62 (“Recent…reported”)
B) The information in lines 62-64 (“These…hibernation”)
C) The information in lines 64-65 (“Lolling…circulation”)
D) The information in lines 67-68 (“It’s… strokes”)

28 Which statement about the effect of hibernation on the seven bears is best supported by the graph?
A) Only one of the bears did not experience an appreciable change in its total plasma cholesterol level.
B) Only one of the bears experienced a significant increase in its total plasma cholesterol level.
C) All of the bears achieved the desirable plasma cholesterol level for humans.
D) The bear with the lowest total plasma cholesterol level in its active state had the highest total plasma cholesterol level during hibernation.

================

Questions 38-47 are based on the following passages.

Passage 1 is adapted from Stewart Brand, “The Case for Reviving Extinct Species.” ©2013 by the National Geographic Society. Passage 2 is adapted from the editors at Scientific American, “Why Efforts to Bring Extinct Species Back from the Dead Miss the Point.” ©2013 by Nature America, Inc.

Passage 1: Many extinct species—from the passenger pigeon to the woolly mammoth—might now be reclassified as “bodily, but not genetically, extinct.” They’re dead, but their DNA is recoverable from museum specimens and fossils, even those up to 200,000 years
old. Thanks to new developments in genetic technology, that DNA may eventually bring the animals back to life. Only species whose DNA is too old to be recovered, such as dinosaurs, are the ones to consider totally extinct, bodily and genetically.

But why bring vanished creatures back to life? It will be expensive and difficult. It will take decades. It won’t always succeed. Why even try? Why do we take enormous trouble to protect endangered species? The same reasons will apply to species brought back from extinction: to preserve biodiversity, to restore diminished ecosystems, to advance the science of preventing extinctions, and to undo harm that humans have caused in the past.

Furthermore, the prospect of de-extinction is profound news. That something as irreversible and final as extinction might be reversed is a stunning realization. The imagination soars. Just the thought of mammoths and passenger pigeons alive again
invokes the awe and wonder that drives all conservation at its deepest level.

Passage 2: The idea of bringing back extinct species holds obvious gee-whiz appeal and a respite from a steady stream of grim news. Yet with limited intellectual bandwidth and financial resources to go around, de-extinction threatens to divert attention from the modern biodiversity crisis. According to a 2012 report from the International Union for
Conservation of Nature, some 20,000 species are currently in grave danger of going extinct.

Species today are vanishing in such great numbers—many from hunting and habitat destruction—that the trend has been called a sixth mass extinction, an event on par with such die-offs as the one that befell the dinosaurs 65 million years ago.
A program to restore extinct species poses a risk of selling the public on a false promise that technology alone can solve our ongoing environmental woes — an implicit assurance that if a species goes away, we can snap our fingers and bring it back.

Already conservationists face difficult choices about which species and ecosystems to try to save, since they cannot hope to rescue them all. Many countries where poaching and trade in threatened species are rampant either do not want to give up the revenue or lack the wherewithal to enforce their own regulations. Against that backdrop, a costly and flamboyant project to resuscitate extinct flora and fauna in the name of conservation looks irresponsible: Should we resurrect the mammoth only to let elephants go under? Of course not.

That is not to say that the de-extinction enterprise lacks merit altogether. Aspects of it could conceivably help save endangered species. For example, extinct versions of genes could be reintroduced into species and subspecies that have lost a dangerous amount of genetic diversity, such as the black-footed ferret and the northern white rhino. Such investigations, however, should be conducted under the mantle of preserving modern biodiversity rather than conjuring extinct species from the grave.

38. The author of Passage 1 suggests that the usefulness of de-extinction technology may be limited by the
A) amount of time scientists are able to devote to genetic research.
B) relationship of an extinct species to contemporary ecosystems.
C) complexity of the DNA of an extinct species.
D) length of time that a species has been extinct.

39. Which choice provides the best evidence for the answer to the previous question?
A) Lines 7-9 (“Thanks… life”)
B) Lines 9-11 (“Only… genetically”)
C) Line 13 (“It will be… difficult”)
D) Lines 13-14 (“It will take… succeed”)

40. As used in line 27, “deepest” most nearly means
A) most engrossing.
B) most challenging.
C) most extensive.
D) most fundamental.

41. The authors of Passage 2 indicate that the matter of shrinking biodiversity should primarily be considered a
A) historical anomaly.
B) global catastrophe.
C) scientific curiosity.
D) political problem.

42. Which choice provides the best evidence for the answer to the previous question?
A) Lines 37-41 (“Species… ago”)
B) Lines 42-45 (“A program… woes”)
C) Lines 53-56 (“Against… irresponsible”)
D) Lines 65-67 (“Such… grave”)

43. As used in line 37, “great” most nearly means
A) lofty.
B) wonderful.
C) large.
D) intense.

44. The reference to the “black-footed ferret and the northern white rhino” (line 64) serves mainly to
A) emphasize a key distinction between extinct and living species.
B) account for types of animals whose numbers are dwindling.
C) provide examples of species whose gene pools are compromised.
D) highlight instances of animals that have failed to adapt to new habitats.

45. Which choice best states the relationship between the two passages?
A) Passage 2 attacks a political decision that Passage 1 strongly advocates.
B) Passage 2 urges caution regarding a technology that Passage 1 describes in favorable terms.
C) Passage 2 expands on the results of a research study mentioned in Passage 1.
D) Passage 2 considers practical applications that could arise from a theory discussed in Passage 1.

46. How would the authors of Passage 2 most likely respond to the “prospect” referred to in line 21, Passage 1?
A) With approval, because it illustrates how useful de-extinction could be in addressing widespread environmental concerns.
B) With resignation, because the gradual extinction of many living species is inevitable.
C) With concern, because it implies an easy solution to a difficult problem.
D) With disdain, because it shows that people have little understanding of the importance of genetic diversity

47. Which choice would best support the claim that the authors of Passage 2 recognize that the “imagination soars” (line 24, Passage 1) in response to de-extinction technology?
A) Lines 28-30 (“The… news”)
B) Lines 30-33 (“Yet… crisis”)
C) Lines 58-59 (“That… altogether”)
D) Lines 61-63 (“For… diversity”)

================

Questions 12-22 are based on the following passage and supplementary material: Vanishing Honeybees: A Threat to Global Agriculture

Honeybees play an important role in the agriculture industry by pollinating crops. An October 2006 study found that as much as one-third of global agriculture depends on animal pollination, including honeybee pollination—to increase crop output. The importance of bees highlights the potentially disastrous affects of an emerging, unexplained crisis: entire colonies of honeybees are dying off without warning. They know it as colony collapse disorder (CCD), this phenomenon will have a detrimental impact on global agriculture if its causes and solutions are not determined.

Since the emergence of CCD around 2006, bee mortality rates have exceeded 25 percent of the population each winter. There was one sign of hope: during the 2010–2012 winter seasons, bee mortality rates decreased slightly, and beekeepers speculated that the colonies would recover. Yet in the winter of 2012–2013, 10 percent in the United States, with a loss of 31 percent of the colonies that pollinate crops.

12 A) NO CHANGE
B) pollination: this is
C) pollination,
D) pollination;

13 A) NO CHANGE
B) highlights the potentially disastrous effects
C) highlight the potentially disastrous effects
D) highlight the potentially disastrous affects

14 A) NO CHANGE
B) Known as colony
C) It is known as colony
D) Colony

15 Which choice offers the most accurate interpretation of the data in the chart?
A) NO CHANGE
B) been above the acceptable range.
C) not changed noticeably from year to year.
D) greatly increased every year.

16 Which choice offers an accurate interpretation of the
data in the chart?
A) NO CHANGE
B) portion of bees lost was double what it had been
the previous year, rising to
C) number of losses, which had fallen within the
acceptable range the previous year, rose to
D) portion of total colonies lost rose almost 10 percentage points, with a loss of

Honey Bee Colony Loss graph

Studies have offered several possible reasons that bees are vanishing. One reason that is often cited is the use of pesticides called neonicotinoids, which are absorbed by plants and linger much longer than do topical pesticides. Chemicals such as herbicides and
fungicides may also play a role, contaminating the pollen that bees typically feed on and inhibiting healthy insect maturation.

17 Which choice most smoothly and effectively introduces the writer’s discussion of studies of CCD in this paragraph?

A) NO CHANGE
B) Bees are vanishing, and according to studies there are several possible reasons for this trend.
C) Several possible reasons, offered by studies, may explain why bees are vanishing.
D) DELETE the underlined sentence.

18 At this point, the writer is considering adding the following sentence. Prolonged exposure to neonicotinoids has been shown to increase bees’ vulnerability to disease and parasitic mites. Should the writer make this addition here?

A) Yes, because it provides support for the claim made in the previous sentence.
B) Yes, because it introduces a new idea that will become important later in the passage.
C) No, because it would be better placed elsewhere in the passage.
D) No, because it contradicts the main idea of the passage.

Given the role that honeybees play in agriculture, the impact of this loss of hives on fruit, vegetable, seed, and nut crops is not to be scoffed at. A reduction in bee numbers leads to less pollination, which in turn leads to smaller harvests and higher food prices. Some farmers have resorted to renting hives from beekeepers to pollinate their crops; when there is a shortage of bees this being an expensive proposition. Other farmers have
increased they’re dependence on costly hand-pollination by human workers.

urthermore, there may be sociological repercussions. Agroecologist Alexandra-Maria Klein has suggested that rising produce prices could lead to an increase in obesity as people turn to cheaper, less wholesome fare.

Though the precise causes of CCD are yet unclear, some commonsense measures may be taken. A decrease in the use of certain pesticides, herbicides, and fungicides, as well as greater attention to the nutrition, habitat, and genetic diversity of managed hives, could begin a shift in a favorable direction.

19
A) NO CHANGE
B) is a pretty big deal.
C) can’t be put on the back burner.
D) cannot be ignored.

20
A) NO CHANGE
B) crops, this is an expensive proposition when
there is a shortage of bees.
C) crops, an expensive proposition when there is a shortage of bees.
D) crops; an expensive proposition when there is a shortage of bees.

21
A) NO CHANGE
B) there
C) their
D) its

22
The writer wants a conclusion that addresses the future of efforts to combat CCD. Which choice results in the passage having the most appropriate concluding sentence?

A) NO CHANGE
B) Still, bee colonies have experienced such devastating losses that the consequences of the issue have been felt worldwide.
C) Although CCD is a relatively new phenomenon, scientists have been studying other aspects of honeybees for over a century.
D) Genetic variation in bee colonies generally improves bees’ productivity, disease resistance, and ability to regulate body temperature.

================

Fall 2016 PSAT Practice Test

Click to access psat-nmsqt-practice-test-2.pdf

Questions 39-47 are based on the following passage.
This passage is adapted from Ed Yong, “Gut Bacteria Allows Insect Pest to Foil Farmers.” ©2013 by National Geographic Society.

Here is a lesson that we’re going to be taught again and again in the coming years: Most animals are not just animals. They’re also collections of Line microbes. If you really want to understand animals, 5 you’ll also have to understand the world of microbes inside them. In other words, zoology is ecology.

Consider the western corn rootworm—a beetle that’s a serious pest of corn in the United States. The adults have strong preferences for laying eggs in corn 10 fields, so that their underground larvae hatch into a feast of corn roots. This life cycle depends on a
continuous year-on-year supply of corn. Farmers can use this dependency against the rootworm, by planting soybean and corn in alternate years. 15 These rotations mean that rootworms lay eggs into corn fields but their larvae hatch among soybean, and die.

But the rootworms have adapted to this strategy by reducing their strong instincts for laying eggs in 20 corn. These rotation-resistant females might lay among soybean fields, so their larvae hatch into a crop of corn.

There are almost certainly genetic differences that separate the rotation-resistant rootworms from their 25 normal peers, but what are they? Researchers at the University of Illinois have been studying the problem since 2000 and, despite generating a vast mountain of data, have failed to find the genes in question. “The western corn rootworm has been an enigma for 30 a long time,” says Manfredo Seufferheld. “This insect has the ability to adapt to practically all control methods deployed against it, including crop rotation.

After many years of research about the mechanisms of rotation resistance, results were mostly 35 inconclusive.” So, Seufferheld looked elsewhere. Rather than focusing on the rootworm’s own genes, he studied the genes of the bacteria in its gut . . . and found
some answers. The rotation-resistant varieties have 40 very different gut bacteria from the normal ones. And when the team killed these microbes with antibiotics, they severely reduced the beetle’s ability to cope with rotation.

“The bad guy in the story—the western corn 45 rootworm—was actually part of a multi-species conspiracy,” says Joe Spencer, who was part of the study.

The team, including graduate student Chia-Ching Chu, found that a third of the rootworms’ gut 50 bacteria comprise species that are unique to either the resistant or normal varieties. These two factions also differ in the relative numbers of the bacteria that they share.

These different microbes give the resistant beetles 55 an edge when eating soybeans. The rootworms digest the protein in their meals using enzymes called cysteine proteases, and soybeans defend themselves with substances that can block these enzymes.

But Chu found that the more the beetles’ bacteria 60 differed from the normal set, the higher the levels of cysteine proteases in their guts. By avoiding indigestion, these beetles were better at surviving among soybeans, and more likely to lay their eggs there.

65 The team proved that the bacteria were responsible by killing them with antibiotics. Sure enough, this drastically lowered the cysteine protease activity in the guts of the rotation-resistant beetles and wrecked their ability to thrive among soybeans.

39. Over the course of the passage, the main focus shifts from a
A) statement about the challenge posed by a particular insect to an indication of why that
challenge was easy to overcome.
B) summary of a once-unexplained natural phenomenon to a biography of the scientists
who researched that phenomenon.
C) description of a problem affecting agriculture to an explanation of how scientists identified the cause of that problem.
D) discussion about a scientific field to an anecdote showing how research is done in that field.

40. The statement “zoology is ecology” (line 6) mainly serves to
A) propose that two areas of scientific knowledge be merged.
B) point out that knowledge obtained in one field of research will lead to expertise in another.
C) assert a point about biological science that is supported by the example in the passage.
D) suggest that one field of scientific research has completely supplanted another.

41. According to the passage, one similarity between rotation-resistant rootworms and normal rootworms is that they both
A) reduce crop productivity by extracting nutrients from the soil.
B) produce larvae that feed on the plant roots of crops.
C) adapt to crop rotation by maintaining high levels of enzymes in their guts.
D) contain the same quantity and composition of bacteria in their guts.

42. Which choice most clearly provides information indicating how some rootworms have overcome farmers’ efforts to eradicate them?

A) Lines 15-17 (“These… die”)
B) Lines 18-20 (“But… corn”)
C) Lines 25-28 (“Researchers… question”)
D) Lines 41-43 (“And… rotation”)

43. The central claim in the fourth paragraph (lines 23-35) is that

A) extensive study of the rootworm’s genes was insufficient to determine why some rootworms are rotation resistant.
B) the rootworm’s ability to adapt to pest control methods is unique among insects.
C) the genetic profile of rootworms is significantly more complex than researchers initially believed.
D) our current understanding of genetics is inadequate to allow researchers to understand why some rootworms are rotation resistant.

44. As used in line 24, “separate” most nearly means
A) distinguish.
B) discharge.
C) extract.
D) scatter.

45. According to the passage, the gut bacteria of rotation-resistant rootworms

A) help the rootworms survive in soybean crops.
B) are responsible for lowering the amount of cysteine protease in the rootworms’ guts.
C) make the rootworms less vulnerable to being killed by antibiotics.
D) are transferred to the larvae that hatch from the rootworms’ eggs.

46. Which choice provides the best evidence for the answer to the previous question?
A) Lines 29-30 (“The western… Seufferheld”)
B) Lines 39-40 (“The rotation-resistant… ones”)
C) Lines 44-47 (“The bad… study”)
D) Lines 54-55 (“These… soybeans”)

47. The main idea of the last paragraph is that

A) cysteine proteases are harmful to rootworms when present in large quantities in the body.
B) eggs laid by rotation-resistant rootworms will hatch into crops of soybeans.
C) bacteria unique to rotation-resistant rootworms allow them to digest soybeans.
D) rotation-resistant rootworms do not digest soybeans using cysteine proteases.

================

Click to access psat-nmsqt-practice-test-2.pdf

Questions 12-22 are based on the following passage and supplementary material.
A Study in Arctic Migration

Each year, many species of shorebirds migrate from locations in the Southern Hemisphere to their breeding grounds in the 12 Arctic. A journey of thousands of
kilometers that requires frequent stops to fuel up. The risk of death is significant, and the Arctic is an inhospitable region for most of the 13 year, yet the shorebirds never failing to make their annual pilgrimage.

Come spring, the Arctic becomes a suitable habitat, providing many benefits: an abundant supply of food, permanent daylight, ample nesting space, fewer pathogens, and fewer predators to invade the nests of these ground-dwelling birds. These benefits are found in all regions of the 14 Arctic regardless of latitude yet some shorebirds continue on to the high Arctic. If these birds are simply looking for open space and enough food to eat, then why not end their long journey in the low Arctic? Continuing on to the north requires more fuel and carries an even greater risk of 15 mortality if the
birds continue on. The most likely reason certain shorebirds head to the high Arctic is to escape their predators.

12
A) NO CHANGE
B) Arctic, a
C) Arctic; a
D) Arctic; which is a

13
A) NO CHANGE
B) year, the shorebirds never fail
C) year, yet the shorebirds never fail
D) year; yet the shorebirds never failing

14
A) NO CHANGE
B) Arctic, regardless of latitude
C) Arctic, regardless of latitude,
D) Arctic: regardless of latitude,

15
A) NO CHANGE
B) mortality if they keep going.
C) mortality and death.
D) mortality.

[1] A four-year study by a team of Canadian scientists, headed by student Laura McKinnon of the Université du Québec, 16 provide evidence in support of this hypothesis. [2] The scientists created artificial nests that resembled a typical shorebird’s nest. [3] Then each year, during the shorebirds’ breeding season, forty of the nests were placed in each of seven locations that ranged in latitude from the low Arctic to the high Arctic. [4] Each nest had been baited with four 17 quail egg’s, which are similar in size and shape to a shorebird’s eggs. [5] The scientists returned to the nests many times over nine days to check how many eggs remained in the nests. [6] A nest was said to have survived if, at the end of the nine days, it contained at least one undisturbed quail egg.

16
A) NO CHANGE
B) provides
C) are providing
D) have provided

17
A) NO CHANGE
B) quail eggs,
C) quail eggs’,
D) quails eggs,

To make this paragraph most logical, sentence 5 should be placed
A) where it is now.
B) after sentence 1.
C) after sentence 2.
D) after sentence 6

Nest survival by site

The figure shows the results for the nesting 19 sites,
furthermore, at four of the seven locations, averaged over
the four years of the study. The 20 number of predators
invading the nests increased over time at each location.
This result confirmed that predators were present at the
researchers’ chosen locations. The researchers found that
the percent of 21 surviving nests was greater at locations
having higher latitudes. For example, on day 9,
approximately 55 percent of nests were found to have
survived at the 82°N location compared to approximately 10 percent of nest survival at the 63°N location. This study provides the first known quantifiable evidence for the previously unanswered question of why shorebirds
continue on to the high Arctic. 22 The shorebirds risk
their own survival by flying farther. Their offspring have a better chance of survival because fewer predators invade the nests.

================

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Sample tests

2015 Practice Test PSAT/NMSQT

 

Related topics

PSAT History/Social studies questions

PSAT World Literature questions

Good hypothesis vs bad hypothesis

In science, what is the difference between a good and a bad hypothesis A hypothesis is something actually testable. Consider these examples:

A. Someone claims “lightning is caused by angry ghosts.” If true then you’d predict that when ghosts are angry, there’d be more lightning.

But this can’t be tested.There is no way to determine whether ghosts are angry – or whether their wrath is correlated with thunderstorms.

We can’t measure ghosts so there are no testable predictions. It is thus not a good hypothesis.

 

B. Someone claims “lightning is caused by electrical charges moving from the ground to the clouds.” If true then you’d predict that when there is an imbalance of electrically charged particles (electrons) then electrons might move from one place to another.

We can measure electrical charges. The idea is testable so it is a good hypothesis.

cause of lightning electrical charges

C. Someone claims “Planets orbit the Sun at different speeds, because speed is related to the gravitational pull of the Sun, and the further away a planet from the Sun is, the less of a pull it feels. If its true then you’d predict that planets like Mercury are pulled more, and move faster.

This can be tested. We do have ways to measure gravitational pull, distance from the Sun, and speed. Since it makes testable predictions, it is a good hypothesis.

Distinguishing Fact, Opinion, Belief, Prejudice, and Stereotypes

Adapted from: Fowler, H. Ramsey. The Little, Brown Handbook. Boston: Little, Brown, 1986

It's Ok to change your opinion evidence

Neil Degrasse Tyson

Facts

are verifiable things that really occurred, or are actually true.

We can determine whether it is true by researching, by examining evidence. This may involve numbers, dates, testimony, etc. (Ex.: “World War II ended in 1945.”) The truth of the fact is beyond argument if the measuring devices, or records, or memories, are correct. Facts provide crucial support for the assertion of an argument.

In science, a fact is a repeatable careful measurement (by experimentation or other means), also called empirical evidence.

In history,historical fact is a fact about the past. It answers the very basic question, “What happened?” Yet beyond merely listing the events in chronological order, historians try to discover why events happened, what circumstances contributed to their cause, what subsequent effects they had. – Norman Schulz

Facts by themselves are often meaningless until we put them in context, draw conclusions, and, thus give them meaning.

Opinions

are judgments based on facts. Opinions should be an honest attempt to draw a reasonable conclusion from factual evidence.

For example, we know that millions of people go without proper medical care, and so one could form the opinion that the country should institute national health insurance, even though it would cost billions of dollars.

An opinion should be changeable: in science we are actually supposed to change our views if we have new evidence

By themselves, opinions have little power to convince. You must let your reader know what your evidence is, and how it led you to arrive at your opinion.

Beliefs

are convictions based on cultural or personal faith, morality, or values. Statements such as “Capital punishment is legalized murder” express viewpoints, but are not based on facts or evidence. Beliefs cannot be disproved. Since beliefs are inarguable, they cannot serve as the thesis of a formal argument.

There is nothing wrong with having beliefs – we all have them. But we should be careful to distinguish between opinions and beliefs – or clearly explain to the reader what our view is, and what is based on. – RK

Prejudices

are opinions based on insufficient or unexamined evidence. Example “Most women are bad drivers.”

Unlike a belief, a prejudice is testable: it can be analyzed on the basis of facts.

To some extent, all people form some prejudices, or accept them from others – family, friends, the media, etc. – without testing their truth.

At best, prejudices are oversimplifications. At worst, they reflect a narrow-minded view of the world. They are not likely to win the confidence or agreement of your readers.

Also (not from the book by Fowler & Ramsey)

Stereotypes – a probabilistic assumption about individuals based on their group membership

While not universally valid, they can be statistically accurate generalizations about how a group of people behaves. Unlike a belief, a stereotype is testable: it can be analyzed on the basis of facts.

Bayes’ theorem provides a framework for understanding how individuals might update their beliefs about groups (stereotypes) based on new evidence or data: One can combine prior beliefs with new data to create updated posterior beliefs, However, even with new evidence, stereotypes can be resistant to change because individuals may prioritize information that confirms their prior beliefs and disregard conflicting evidence.

Some research suggests that many stereotypes demonstrate a high degree of accuracy when empirically tested, often exceeding the average effect size in social psychology. This perspective acknowledges that while stereotypes may be associated with negative social consequences, it does not mean they are inherently inaccurate.

– Jussim, L. (2012). Social Perception and Social Reality: Why Accuracy Dominates Bias and Self-Fulfilling Prophecy. Oxford University Press.

– Jussim, L., Cain, T. R., Crawford, J. T., Harber, K. D., & Cohen, F. (2009). The unbearable accuracy of stereotypes. In T. D. Nelson (Ed.), Handbook of prejudice, stereotyping, and discrimination (pp. 199–227). Psychology Press.

– Ryan, C. S. (2002). Stereotype accuracy. European Review of Social Psychology, 12(1), 75–109. https://doi.org/10.1080/14792772143000029

A problem arises when probability-based assumptions are applied rigidly to individuals, leading to biased judgments and unfair treatment. https://pmc.ncbi.nlm.nih.gov/articles/PMC9337700/

__________________________________

Here are the classic Greek philosophers, who developed rationalist philosophy: a critical, systematic system – reasoned argument – to distinguish between facts, beliefs and opinions.

Pindar_Xenophanes_Anaxagoras_Socrates_Plato_Aristotle_800

Is evolution a theory or a fact

Is evolution a theory or a fact?

“evolution” has 2 different uses:
‘facts’ of evolution, and the ‘theory’ of evolution.

Here are observable facts

* Many forms of life that used to exist, no longer exist today.
(We’ve found many fossils; more are discovered every day)

* Many forms of life exist now, that did not exist in the past.
(Many modern animals and plants are obviously different from fossils)

* DNA exists.

* Every time an organism reproduces, random changes (mutations) in DNA happen. (We actually explicitly see these with gene-sequencing)

* Some mutations help an organism survive – those genes pass on to the next generation.
(We actually see organisms survive and reproduce. We can sequence the DNA of the parent and of the offspring. We literally see the genes.)

* Some mutations don’t help an organism survive; those genes die out.
(We actually see that some organisms die before they reproduce. Their genes literally die with them.)

* Millions of different DNA samples show a relationship between all forms of life.

* As time goes by, some genes become more common, some become less common. (This has been directly observed in bacteria, some plants and some animals)

Here is the theory that connect such facts

1. Organisms produce more offspring than can survive to adulthood and reproduce.

2. All organisms have random mutations.

3a. Mutations that allow an organism to survive are passed on to their offspring.

3b. Mutations that don’t allow an organism to survive die off.

4. So over time, some mutations become more common.

The “theory” of evolution is the relationship between observations (“facts.”)

In this sense, the theory is just as true as the theory of gravity, or the theory of electricity.

 

Resources

Evolution 101. Univ of California Museum of Paleontology

http://www.pbs.org/wgbh/nova/labs/lab/evolution/

https://lifeonearth.seas.harvard.edu/learning-activities/

How do we know what DNA looks like

Question: How do we know what DNA and genes really look like?

We see images in books that look like this, but each individual atom is only a nanometer (1 x 10 -10 m) wide.

No visible light microscope can view objects made with such small pieces.

dna-notes-7-728

 

So the real way that we figured out the atom-by-atom structure of DNA is through a technique called X-ray crystallography.

Our molecule of interest – in this case, DNA – is concentrated and crystallized.

It is placed in front of an X-ray source.

The X-rays scatter off the DNA’s atoms. We capture this diffraction pattern on film (or on a digital X-ray detector.)

Photo 51 DNA Diffraction pattern

X-ray diffraction image of the double helix structure of the DNA molecule, taken 1952 by Raymond Gosling, commonly referred to as “Photo 51”, during work by Rosalind Franklin on the structure of DNA (text Wikipedia)

This diffraction pattern is beautiful but doesn’t directly look like the original molecule.

There is a mathematical relationship between the placement of the atoms, and where the atoms deflect – just like there is a relationship between hitting pool balls and how they deflect:

When you know how a pool table is set up, what balls are made of, and see how the balls move after being it, you could use math to work backwards to figure out where the balls originally where.

Billiards Pool

from Banks and Kicks in Pool and Billiards, Dr. Dave Alciatore, Billiards and Pool Principles, Techniques, Resources

The same is true here: We can use math to figure out where each individual atom in the DNA is! Let’s follow the steps below:

On the left, we see X-rays leave a source. Some of these x-rays pass through a lead screen.

The X-rays hit a crystallized DNA sample.

The X-rays bounce off of the molecules, like how pool balls bounce off of each other.

Some of the x-rays bounce onto a film plate. This makes an image.

We end up with a diffraction pattern on film.

How does one physically interpret diffraction patterns in DNA?

DNA X-ray crystallography

Figure 11.4, Purves’s Life: The Science of Biology, 7th Edition

Once we have a diffraction pattern, we then use math to work backwards, and figure out where the atoms must have been.

The result is an electron density map which almost exactly traces out the shape of the molecule.

X Ray crystallography and electron density map

Left image: X-ray diffraction pattern, Wikimedia. Right upper image: electron density map. Right lower image: model fitting atoms to the density map.

Can we image DNA more directly?

Yes. One can use a scanning tunneling microscope (STM).) It shows detail at the the atomic level.  Along with the following image please read Livescience: DNA directly-photographed-for-first-time.html

Photo of DNA helix

DNA’s double-helix seen in electron microscope photograph. By Enzo Di Fabrizio, Magna Graecia University in Catanzaro, Italy.

 

Here is another STM image of DNA. You can see how closely it matches the model from X-ray crystallography.

STM image of DNA

External resources

Are there true pictures of the DNA molecule (not synthetic images), showing the double helix?

On DNA’s Anniversary: How Rosalind Franklin Missed the Helix

Sexism in science: did Watson and Crick really steal Rosalind Franklin’s data?.

The Big Dig

What are we learning?

We’re studying the engineering – applied physics – used in Boston’s Big Dig. We’ll study the effect of changing forces, loads, materials and shapes, on a structure.

Why are we learning this?

To learn how to break a complex real-world problem – building safe tunnels and related structures – into smaller parts that can be solved using scientific/engineering principles.

To learn how to use a simple computer simulation to model such systems.

Vocabulary goals

compression, tension, bending, shear, torsion, loads, dead load, live load, settlement load, thermal load, wind load, earthquake load, dynamic load, arch, brace, buttress

Historical background

The Central Artery/Tunnel Project (CA/T) – the Big Dig – was a megaproject in Boston that rerouted the Central Artery of Interstate 93, the chief highway through the heart of the city, into the 3.5-mile (5.6 km) Thomas P. O’Neill Jr. Tunnel. It also included the construction of the Ted Williams Tunnel (extending Interstate 90 to Logan International Airport), the Zakim Bunker Hill Memorial Bridge over the Charles River, and the Rose Kennedy Greenway in the space vacated by the previous I-93 elevated roadway. Planning began in 1982; construction work was carried out between 1991 and 2006.

  • Intro adapted from Wikipedia, The Big Dig, 1/18

Photo gallery

Here are before-and-after photos of downtown Boston, showing the removal of the Central Artery and it’s replacement with the Rose Kennedy Greenway.

Left-click on it to open in a new window, at higher-resolution.

Boston The Big Dig Before and After (no source found)

Our app Building Big: Forces & Engineering app (from PBS)

Use the worksheet assigned by the teacher.

Building the tunnel under Forth Point Channel

William Harris, in “How Tunnels Work: The Big Dig” (How Stuff Works) writes:

A few miles west, Interstate 90 enters another tunnel that carries the highway below South Boston. Just before the I-90/I-93 interchange, the tunnel encounters the Fort Point Channel, a 400-foot-wide body of water that provided some of the biggest challenges of the Big Dig.

Engineers couldn’t use the same steel-tube approach they employed on the Ted Williams Tunnel because there wasn’t enough room to float the long steel sections under bridges… Eventually, they decided to abandon the steel-tube concept altogether and go with concrete tunnel sections, the first use of this technique in the United States.

…workers first built an enormous dry dock on the South Boston side of the channel. Known as the casting basin, the dry dock measured 1,000 feet long, 300 feet wide and 60 feet deep — big enough to construct the six concrete sections that would make up the tunnel…

The completed sections were sealed watertight at either end. Then workers flooded the basin so they could float out the sections and position them over a trench dredged on the bottom of the channel.

[They couldn’t] simply lower concrete sections into the trench [because] of the MBTA’s Red Line subway tunnel, which runs just under the trench. The weight of the massive concrete sections would damage the older subway tunnel if nothing were done to protect it. So engineers decided to prop up the tunnel sections using 110 columns sunk into the bedrock. The columns distribute the weight of the tunnel and protect the Red Line subway, which continues to carry 1,000 passengers a day.

Fort Point Channel in Boston

Apps

Slider photo: Boston before- and after- Big Dig (10 years later, did the Big Dig deliver?, Boston Globe)

Documentaries

Extreme Engineering: Boston’s Big Dig (2003)

https://vimeo.com/30626123

Tour of the Big Dig in Boston, Bob Vila

National Geographic MegaStructures Boston Big Dig Documentary 2016

https://www.youtube.com/watch?v=R2HHmWxGRMQ

Big Dig The Construction Story of Boston Big Dig

Underground Utility Protection

In “The Big Dig: Learning from a Mega Project”, Virginia Greiman writes

To protect against losses caused by the disruption and failure of underground utilities, a Big Dig utility program relocated 29 miles of gas, electric, telephone, sewer, water, and other utility lines maintained by thirty-one separate companies in 1996.

Some of this infrastructure was more than 150 years old; a complete lack of knowledge on the age, condition, and location of most of the utilities required submission of “as-built” drawings by all project contractors—drawings of existing conditions rather than planned or proposed construction.

The project had to deal with utilities that were shown on as-built drawings but never installed, and damage and flooding caused by underground sewer pipes not identified on the drawings.

Resources

Wikipedia.org: Big Dig

PBS: Great Projects – The Building of America

Archaeology of the Central Artery Project: Highway to the Past. Website + 58 page PDF book.

Big Dig: Massachusetts Historical Commission, Archaeological Exhibits Online

Learning Standards

2016 Massachusetts Curriculum Framework High School Technology/Engineering

HS-ETS1-1. Analyze a major global challenge to specify a design problem that can be improved. Determine necessary qualitative and quantitative criteria and constraints for solutions, including any requirements set by society.

HS-ETS1-2. Break a complex real-world problem into smaller, more manageable problems that each can be solved using scientific and engineering principles.

HS-ETS1-3. Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, aesthetics, and maintenance, as well as social, cultural, and environmental impacts.

HS-ETS1-4. Use a computer simulation to model the impact of a proposed solution to a complex real-world problem that has numerous criteria and constraints on the interactions within and between systems relevant to the problem.

HS-ETS1-5(MA). Plan a prototype or design solution using orthographic projections and isometric drawings, using proper scales and proportions.

HS-ETS1-6(MA). Document and present solutions that include specifications, performance results, successes and remaining issues, and limitations.

 

Chromosomes in cells

What do we need to know about chromosomes? Look inside any form of life – plants, animals, even fungi.

We see individual cells.

Looking more closely, cells have a nucleus.

 

Zoom in on the nucleus and break it open:

Here the nucleus has been punctured, objects are spilling out.

These objects are called chromosomes.

Let’s look at them even more closely: They are made of a really thin thread, wrapped up again and again to make a shape.

Zoom in even more – this thread has the shape of a helix (spiral shape.)

Wait – not just one helix, but two – wrapped around each other.

This shape is called a double helix.

This beautiful molecule here is DNA.

Those letters – T, C, A, and G – are just abbreviations for molecules (“DNA bases.)

A more realistic drawing would show the shape of these DNA bases (see top part of this next diagram, but that’s a lot to draw.)

To make it easier to draw we usually just write the letters (see bottom part of this diagram.)

So now we have discovered the relationship between DNA and chromosomes.

DNA is a very thin, long chemical, made of many little DNA bases.

These units are wound up into two helixes, and then wound up into larger objects, chromosomes.

It’s like how a skein of yarn is made of yarn thread, wound, and wound up again, into a complex and large shape.

Threads of DNA are wound up into a chromosome:

How many chromosomes in each cell?

That depends on the organism:

Image from What’s a Genome, courtesy of http://www.GenomeNews Network.org/J. Craig Venter Institute.
http://www.expeditions.udel.edu/extreme08/genomics/

We see here that humans have 46 chromosomes in almost every cell in our body.

Each chromosome contains many genes, so the total number of genes is huge.

Image from What’s a Genome, courtesy of http://www.GenomeNews Network.org/J. Craig Venter Institute.
http://www.expeditions.udel.edu/extreme08/genomics/

The photograph below is a karyotype: we cut open a cell nucleus, let the chromosomes tumble out, and photograph it.

Then we can cut out each of the chromosome images. Next we line them up, in pairs.

Why pairs? We have two of every chromosome – Half are from one’s mother, and half from one’s father.

And remember that each chromosome has many genes.

So you have 2 copies of every gene (one from each parent)

A pair of matched chromosomes are called “homologous chromosomes.”

Homologous is Greek for “same word,”

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