When can correlation equal causation?
Lesson excerpted from The Logic of Science blog
“Correlation does not equal causation.” … although useful, the phrase can be misleading because it often leads to the misconception that correlation can never equal causation, when in reality there are situations in which you can use correlation to infer causation.
Causality is the actual relationship between causes and effects.
Why correlation doesn’t always equal causation
When X and Y are correlated, why can’t we automatically assume that the change in X is causing the change in Y?
There are four possible explanations for why X and Y would change together:
-
X is causing Y to change
-
Y is causing X to change
-
A third variable (Z) is causing both of them to change
-
The relationship isn’t real and is being caused by chance
[So we] can’t jump to the conclusion that X is causing Y. Further, in most cases, these four possibilities can’t be disentangled. For more details see Why correlation doesn’t have to mean causation
One of my personal favorites is the correlation between ice cream sales and drowning. As ice cream sales increase, so do drowning accidents. Does that mean that eating ice cream is causing people to drown? Of course not. [Clearly] a third variable (time of the year/temperature) is driving both the drowning accidents and the ice cream sales (i.e., people both swim more often and eat more ice cream when it is hot, resulting in a correlation between drowning and eating ice cream that is not at all causal).
Additionally, sometimes two things really do correlate tightly just by chance. The website tylervigen.com has collected a bunch of these, such as the comical correlation between the number of films that Nicholas Cage stars in and the number of drowning accidents in a given year (everything correlates with drowning for some reason)….
Correlation can equal causation
All scientific tests rely on correlation – there is a way to go from correlation to causation: controlled experiments.
If, for example, a scientist does a large, double-blind, randomized controlled trial of a new drug (X) and finds that people who take it have increased levels of Y, we could then say that taking X is correlated with increased levels of Y, but we could also say that taking X causes increased levels of Y.
The key difference is that in this case, we controlled all of the other possibilities such that only X and Y changed. In other words, we eliminated the possibilities other than causation.
[Consider the misleading] correlation between autism rates and organic food sales, but this time let’s say that someone was actually testing the notion that organic food causes autism (obviously it doesn’t, but just go with it for the example).
Therefore, they select a large group of young children of similar age, sex, ethnicity, medication use, etc. They randomly assign half of them to a treatment group that will eat only organic food, and they randomly assign the other half to a control group that will eat only non-organic food.
Further, they blind the study so that none of the doctors, parents, or children know what group they are in. Then, they record whether or not the children develop autism.
Now, for the sake of example, let’s say that at the end, they find that the children who ate only organic food have significantly higher autism rates than those who ate non-organic food. As with the drug example earlier, it would be accurate to say that autism and organic food are correlated, but it would also be fair to say that organic food causes autism (again, it doesn’t, it’s just an example).
So, how is this different than the previous example where we simply showed that, over time, organic food sales and autism rates are correlated? Quite simply, the key difference is that this time, we controlled the confounding factors so that the only differences between the groups were the food (X). Therefore, we have good reason to think that the food (X) was actually causing the autism (Y), because nothing else changed.
Let’s walk through this step by step, starting with the general correlation between organic food sales (X) and autism rates (Y) and looking at each of the four possibilities I talked about earlier.
-
Could organic food be causing autism? Yes
-
Could autism be causing people to buy more organic food? Yes (perhaps families with an autistic family member become more concerned about health and, therefore, buy organic food [note: organic food isn’t actually healthier])
-
Could a third variable be causing both of them? Maybe, though I have difficulty coming up with a plausible mechanism in this particular case.
-
Could the relationship be from chance? Absolutely. Indeed, this is the most likely answer.
Now, let’s do the same thing, but with the controlled experiment.
-
Could the organic diet be causing autism? Yes
-
Could autism be causing the diet? No, because diet was the experimental variable (i.e., the thing we were manipulating), thus changes in it preceded changes in the response variable (autism).
-
Could it be caused by a third variable? No, because we randomized and controlled for confounding variables. This is critically important. To assign causation, you must ensure that the X and Y variables are the only things that are changing/differ among your groups.
-
Could the relationship be from chance? Technically yes, but statistically unlikely.
Is the difference clear now? In the controlled experiment, we could assign causation because changes in X preceded changes in Y (thus Y couldn’t be causing X) and nothing other than X and Y changed. Therefore, X was most likely causing the changes in Y.
That “most likely” clause is an important one that I want to spend a few moments on. Science does not deal in proof, nor does it provide conclusions that we are 100% certain of. Rather, it tells us what is most likely true given the current evidence… The fact that science does not give us absolute certainty does not mean that it is unreliable. Science clearly works, and the ability to assign probabilities is a vast improvement over the utter guesswork that we have without it.
Assigning specific causation when general causation has already been established
Next, I want to talk about causes where you can use a correlation between X and Y as evidence of causation based on an existing knowledge of causal relationships between X and Y.
In other words, if it is already known that X causes Y, then you can look at specific instances where X and Y are increasing together (if it is a positive relationship) and say, “X is causing at least part of that change in Y” (or, more accurately, “probably causing”).
- Smoking and lung/bronchial cancer rates (data via the CDC). P < 0.0001
Let me use an example that I have used before to illustrate this. Look at the data to the right on smoking rates and lung cancer in the US. There is a clear correlation (lung cancer decreases as smoking rates decrease), and I don’t think that anyone would take issue with me saying that the decrease in smoking was probably at least partially the cause for the decrease in lung cancer rates.
Now, why can I make that claim? After all, if we run this through our previous four possibilities, surely we can come up with other explanations.
So, why can I say, with a high degree of confidence, that the smoking rate is probably contributing to the decrease? Quite simply, because a causal relationship between smoking and lung cancer has already been established.
In other words, we already know from previous studies that smoking (X) causes lung cancer (Y). Therefore, we already know that an increase in smoking will cause an increase in lung cancer and a decrease in smoking will cause a decrease in lung cancer.
Therefore, when we look at situations like this, we can conclude that the decrease in smoking is contributing to the decrease in cancer rates because causation has already been established.
To be clear, other factors might be at play as well, and, ideally, we would measure those and determine how much each one is contributing, but even with those other factors, our prior knowledge tells us that smoking should be a causal factor.
This same line of reasoning is what lets us look at things like the correlation between climate change and CO2 and conclude that the CO2 is causing the change. We already know from other studies that CO2 traps heat and drives the earth’s climate. Indeed, we already know that increases in CO2 cause the climate to warm. Therefore, just like in our smoking example, we can conclude that CO2 is a causal factor in the current warming.
Further, in this case, we have also measured all of the other potential contributors and determined that CO2 is the primary one (I explained the evidence in detail with citations to the relevant studies here, here, and here, so please read those before arguing with me in the comments).
The same thing applies to the correlation between vaccines and the decline in childhood diseases. Multiple studies have already established a causal relationship (i.e., vaccines reduce diseases), therefore we know that vaccines were a major contributor to the reduction in childhood diseases (more details and sources here).
Argument from ignorance fallacies
Finally, I want to talk about a common, and invalid, argument that people often use when presenting a correlation as evidence of causation (here I am talking about examples like in the first section where the results aren’t from controlled studies and causation has not previously been established).
I often find that people defend their assertions of causation with arguments like, “well what else could it be?” or “prove that it was something else.” For example, one who is claiming that vaccines cause autism might defend their argument by insisting that unless a skeptic can prove that something else is causing the supposed increase in autism rates, then it is valid to conclude that vaccines are the cause.
There are two closely related logical problems occurring here. The first is known as shifting the burden of proof. The person who is making a claim is always responsible for providing evidence to back up their claim, and shifting the burden happens when, rather than providing evidence in support of their position, the person making the claim simply insists that their opponent has to disprove the claim.
That’s not how logic works. You have to back up your own position, and your opponent is not obligated to refute your position until you have provided actual evidence in support of it.
The second problem is the argument from ignorance fallacy. This happens when you use a gap in our knowledge as evidence of the thing that you are arguing for.
A good example of this would be someone who says, “well you can’t prove that aliens aren’t visiting earth, therefore, they are” or, at the very least, “therefore my belief that they are is justified.”
Do you see how that works? An absence of evidence is just that: a lack of knowledge. You can’t use that lack of knowledge as evidence of something else.
Conclusion
If you can control for all of those other factors and ensure that the changes in X precede the changes in Y and only X and Y are changing, then you can establish causation within the confidence limits of your statistics.
Organelles in depth
Cell membrane
Made of 2 layers of lipids (fats); aka lipid bilayer.
We sometimes see simplified 2D drawings of this.
This drawing shows a small section of the lipid bilayer: 2 layers of lipids and some proteins floating in these lipids.
Cell membrane lipid bilayer Regents diagram http://www.hobart.k12.in.us/jkousen/Biology/cell.htm#plcell_dia_ans
A more accurate visualization would be to show this in three dimensions:
We sometimes see simplified 2D drawings of this. This drawing shows a small section of the lipid bilayer: 2 layers of lipids and some proteins floating in these lipids.
Cell membrane lipid bilayer Regents diagram http://www.hobart.k12.in.us/jkousen/Biology/cell.htm#plcell_dia_ans
Cytoplasm
A thick viscous liquid filling the cell.
All the organelles float in it.
Filled with millions of enzymes, dissolved salt ions, and other chemicals.
Here is a (false color) visualization of proteins floating in a cell’s cytoplasm. Densely packed!
Nucleus
The command-and-control center of the cell.
Chromosomes (made of DNA) are stored in here. In this animation we see DNA in the nucleus, and a copy of it (RNA) leaving the nucleus and going out into the rest of the cell.
Here we see a more realistic image of the nucleus (lower left); we see mRNA copies of DNA coming out of the nucleus through nuclear pores.
Nucleus to ribosomes to ER GIF from NPR: Protein synthesis
Chromosomes
If we magnify a cell we see chunks floating in the nucleus called chromosomes. They are made of a chemical called DNA.
Here we see a cell nucleus being lysed (broken open) and all the chromosomes are spilling out on the right.
The color was added by hand to make it easier to tell them apart. We cut-and-paste each of the chromosomes, number them, and line them up (lower left.)
In humans we find 23 pairs of chromosomes in every cell.
These X shaped chromosomes are not solid; they are like objects made of wound-up yarn.
A chromosome could be unwound into a long, thing string.
This string is made of DNA molecules.
Each section of the chromosome has difference sequences of DNA.
A complete sequence of DNA is called a gene; it is an instruction on how to build a protein.
Mitochondrion
Plural is mitochondria.
Converts energy from food molecules into a form usable by the cell.
Jay Swan http://www.slideshare.net/jayswan http://www.slideshare.net/jayswan/honors-biology-cellular-respiration
and
Jay Swan http://www.slideshare.net/jayswan http://www.slideshare.net/jayswan/honors-biology-cellular-respiration
Ribosomes
Little organic machines that take in amino acids (from our food) and turn them into proteins.
They are very tiny compared to the size of a cell – often seen as mere dots.
Here we see the ribosomes picking up RNA, and using that instruction to build a protein.
Nucleus to ribosomes to ER GIF from NPR: Protein synthesis
Ribosomes struck on an organelle
On the right we can just barely see the ribosomes as small dots stuck to the ER (endoplasmic reticulum.)
On the left we see the ER magnified.
The ribosomes are a bit clearer here (although we still don’t see their details.)
When the ER is covered with ribosomes we call it the “rough ER.”
Darryl Leja, NHGRI Rough endoplasmic reticulum and ribosomes
Other ribosomes float freely in the cytoplasm.
Here we see mRNA copies of DNA coming out of a cell nucleus, and moving to a ribosome floating nearby.
Here’s how we remember this:
ER (endoplasmic reticulum)
This manufactures lipids and proteins.
Like an assembly line which makes our products.
Next, molecules from the ER are packaged into vesicles, and transported to the Golgi apparatus.
Golgi body
This organelle packages proteins into vesicles, tags them with an “address” and send them to their destination.
another image will be here:
Details of Golgi bodies function and organization
From The Cell: A Molecular Approach, 5th ed. Cooper & Hausman. 2009
The Endomembrane system
Here we see the while system, from products leaving the nucleus, going to the ER, then to the Golgi, and then secreted as a vesicle.
In this case the products are going out to the cell membrane (“plasma membrane.)
From Biotech Review YouTube channel.
More details: The endomembrane system is composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell.
Endomembrane system by Mariana Ruiz Villarreal, LadyofHats
Cytoskeleton
These thin protein tubes give the cell its shape and mechanical resistance to deformation.
With the right stains, one can take a beautiful photo of the cytoskeleton.
Lysosome
Contain enzymes that can break down virtually all kinds of biomolecules. Garbage disposal.
Vacuoles
A lipid bag that can store organic molecules.
Chloroplasts
In this movie of plant cells, we some small, green discs moving around: these are chloroplasts.
They contain a light-absorbing pigment (colored molecule), chlorophyll.
This molecules captures the energy from some wavelengths of light.
The plant cell stores this energy in chemical bonds. The plant builds ATP and sugar molecules which store this energy.
In this image we see some chloroplasts floating within a plant cell.
Here we see a single chloroplast, vastly magnified with a TEM (transmission electron microscope.)
We see that there is quite a bit of detail within them.
Cell wall
Note that animal cells don’t have this organelle. Only plants and bacteria have it.
Made of cellulose – a special sugar used to provide structure, and not used for energy.
If the cell membrane is like a balloon, then the cell wall is like a cardboard box around the balloon, protecting it.
Gives strength and support. Allows plants like bamboo and trees to grow tall.
Here we see a typical boxy shaped plant cell, clearly showing the cell wall (green) and the lipid bilayer (yellow, aka plasma membrane.)
Plant cell has a wall adapaproject
Large central vacuole
A membrane that stores watery bags of food or waste molecules.
How do we know what these organelles really look like?
Visualizing cells and organelles in 3D
Sample questions
Feb 2016 MCAS: Which of the following types of organisms have cell walls composed of cellulose?
A. amoebas B. birds C. grasses D. worms
==========
Feb 2016 MCAS. Antibiotics are medicines used to treat bacterial infections in humans. Some antibiotics work by interfering with the bacteria’s ribosomes. Other antibiotics work by interfering with the bacteria’s plasma membrane.
a. Describe the function of the ribosomes and explain why interfering with the ribosomes would kill the bacteria.
b. Describe the function of the plasma membrane and explain why interfering with the plasma membrane [lipid bilayer] would kill the bacteria.
Medicines called antifungals are used to treat infections caused by fungi. One way antifungals work is by targeting cell parts that are present in fungal cells but not in human cells.
c. Identify one cell part other than a ribosome or a plasma membrane that human cells and fungal cells have in common.
d. Describe what would happen to a human cell if the cell part you identified in part (c) were affected by an antifungal. Explain your answer based on the function of the cell part.
==========
External resources
Biology MCAS exams
Previous MCAS exams from the Massachusetts Department of Elementary and Secondary Education
Below you will find each released short-response question, open-response question, and writing prompt that was included on High School Biology MCAS tests; the scoring guide for each question; and a sample of student work at each score point for that question. Taken together, these provide a picture of the expectations for student performance on the MCAS tests.
Special Education accommodations
February 2018 MCAS Biology Test Administration Resources
MCAS Accessibility and Accommodations
SAMPLE MCAS High School Biology Reference Sheet For Students with Accommodation 20
]MCAS Access & Accommodations Manual Spring 2018
MCAS TEST ACCOMMODATIONS FOR STUDENTS WITH DISABILITIES (PDF document)
MCAS Standard Accommodations
Frequent Breaks: The test is administered in short periods with frequent breaks
Time of Day: The test is administered at a time of day that takes into account the student’s medical or learning needs (IEP or 504 plan must specify time of day)
Small Group: The test is administered in a small group setting (no more than 10 students)
Separate Setting: The test is administered in a room other than the one used by the rest of the class
Individual: The test is administered to the student individually
Specified Area: The test is administered with the student seated at the front or other specified area of the room, in a study carrel, or in another enclosed area (IEP or 504 plan must specify where)
Familiar Test Administrator: The test is administered by a test administrator familiar to the student
Noise Buffers: The student wears noise buffers, after test administration instructions have been read (headphones with music playing are not allowed)
Magnification or Overlays: The student uses magnifying equipment, enlargement devices, colored visual overlays, or specially tinted lenses (IEP or 504 plan must specify which)
Test Directions: The test administrator clarifies general administration instructions No portion of the test items themselves (eg, the introduction to a reading selection) may be read or signed
Large-Print: The student uses a large-print version of the test
Braille: The student uses a Braille version of the test
Place Marker: The student uses a place marker
Track Test Items: The test administrator assists the student in tracking test items (eg, moving from one test question to the next) or by redirecting the student’s attention to the test
Amplification: The student uses sound amplification equipment
Test Administrator Reads Test Aloud (except ELA Reading Comprehension test): Test Administrator reads entire test session word-for-word exactly as written
Test Administrator Reads Test Aloud (except ELA Reading Comprehension test): Test administrator reads selected words, phrases, and/or sentences as directed by the student. The student points to the word, phrase, or sentence that he or she needs read aloud.
Test Administrator Signs Test (except ELA Reading Comprehension test): The test administrator signs the ELA Composition writing prompt or the Mathematics, Science and Technology/Engineering, and/or History and Social Science passages and test items to a student who is deaf or hard of hearing
Electronic Text Reader (except ELA Reading Comprehension test): The student uses an electronic text reader for the ELA Composition writing prompt or the Mathematics and Science and Technology/Engineering tests
Scribe Test (except ELA Composition): For open-response test items (and multiple-choice items if needed), the student dictates responses to a scribe or uses a speech-to-text conversion device to record responses
Organizer, Checklist, Reference Sheet, or Abacus: The student uses a graphic organizer, checklist, individualized mathematics reference sheet, or abacus
Student Signs or Reads Test Aloud: The student reads the test aloud to himself or herself, or student reads the test and records answers on audiotape, then writes responses to test items while playing back the tape; a student who is deaf or hard of hearing signs test items/responses onto video, then writes answers while playing back the tape
Monitor Placement of Responses: The test administrator monitors placement of student responses in the student’s answer booklet
Word Processor: The student uses a word processor, Alpha-Smart, or similar electronic keyboard to type the ELA Composition and/or answers to open-response questions
Answers Recorded in Test Booklet: The student records answers directly in the test booklet
Other Standard Accommodation: Other standard accommodation that is identified by the IEP Team or team, documented in the student’s IEP, and not on this list
Alternate Assessment (Portfolio)
MCAS Nonstandard
Test Administrator Reads Aloud ELA Reading Comprehension Test: The test administrator reads the ELA Reading Comprehension test to a student
Test Administrator Signs ELA Reading Comprehension Test for a Student Who Is Deaf or Hard of Hearing
Electronic Text Reader for the ELA Reading Comprehension Test: The student uses an electronic text reader for the ELA Reading Comprehension test
Scribe ELA Composition: The student dictates the ELA Composition to a scribe or uses a speech-to-text conversion device to record the ELA Composition
Calculation Devices: The student uses a calculator, arithmetic table (including multiplication and division charts), or manipulatives on all sections of the Mathematics or Science and Technology/Engineering test
Spell- or Grammar-Checking Function on Word Processor, Spell-Checking Device, or Word Prediction Software for the ELA Composition: The student uses a spell- or grammar-checking function, spelling device (including hand-held electronic spellers), or word prediction software (IEP must specify which device) for the ELA Composition
Other Nonstandard Accommodation: Other nonstandard accommodation that is identified by the IEP Team or team, documented on the student’s IEP, and not on this list
.
How do point particles create atoms with size?
This article is archived for use with my students from Ask Ethan: If Matter Is Made Of Point Particles, Why Does Everything Have A Size?
Forbes, Stars With a Bang, by Ethan Siegel 9/16/17
Proton Structure Brookhaven National Laboratory
The big idea of atomic theory is that, at some smallest, fundamental level, the matter that makes up everything can be divided no further. Those ultimate building blocks would be literally ἄ-τομος, or un-cuttable.
As we’ve gone down to progressively smaller scales, we’ve found that molecules are made of atoms, which are made of protons, neutrons, and electrons, and that protons and neutrons can be further split into quark and gluons. Yet even though quarks, gluons, electrons, and more appear to be truly point-like, all the matter made out of them has a real, finite size. Why is that? That’s what Brian Cobb wants to know:
Many sources state that quarks are point particles… so one would think that objects composed of them — in this instance, neutrons — would also be points. Is my logic flawed? Or would they be bound to each other in such a way that they would cause the resulting neutron to have angular size?
Let’s take a journey down to the smallest scales, and find out what’s truly going on.
Magdalena Kowalska / CERN / ISOLDE team
If we take a look at matter, things behave similar to how we expect they should, in the macroscopic world, down to about the size of molecules: nanometer (10-9meter) scales. On smaller scales than that, the quantum rules that govern individual particles start to become important.
Single atoms, with electrons orbiting a nucleus, come in at about the size of an Angstrom: 10-10 meters. The atomic nucleus itself, made up of protons and neutrons, is 100,000 times smaller than the atoms in which they are found: a scale of 10-15 meters. Within each individual proton or neutron, quarks and gluons reside.
While molecules, atoms, and nuclei all have sizes associated with them, the fundamental particles they’re made out of — quarks, gluons, and electrons — are truly point-like.
E. Siegel / Beyond The Galaxy
The way we determine whether something is point-like or not is simply to collide whatever we can with it at the highest possible energies, and to look for evidence that there’s a composite structure inside.
In the quantum world, particles don’t just have a physical size, they also have a wavelength associated with them, determined by their energy. Higher energy means smaller wavelength, which means we can probe smaller and more intricate structures. X-rays are high-enough in energy to probe the structure of atoms, with images from X-ray diffraction and crystallography shedding light on what molecules look like and how individual bonds look.
Imperial College London
At even higher energies, we can get even better resolution. Particle accelerators could not only blast atomic nuclei apart, but deep inelastic scattering revealed the internal structure of the proton and neutron: the quarks and gluons lying within.
It’s possible that, at some point down the road, we’ll find that some of the particles we presently think are fundamental are actually made of smaller entities themselves. At the present point, however, thanks to the energies reached by the LHC, we know that if quarks, gluons, or electrons aren’t fundamental, their structures must be smaller than 10-18 to 10-19 meters. To the best of our knowledge, they’re truly points.
Brookhaven National Laboratory
So how, then, are the things made out of them larger than points? It’s the interplay of (up to) three things: Forces, Particle properties, and Energy.
The quarks that we know don’t just have an electric charge, but also (like the gluons) have a color charge. While the electric charge can be positive or negative, and while like charges repel while opposites attract, the force arising from the color charges — the strong nuclear force — is always attractive. And it works, believe it or not, much like a spring does.
Warning: Analogy ahead!
Here we go:
How did the Proton Get Its Spin? Brookhaven National Laboratory
Above: The internal structure of a proton, with quarks, gluons, and quark spin shown. The nuclear force acts like a spring, with negligible force when unstretched but large, attractive forces when stretched to large distances
When two color-charged objects are close together, the force between them drops away to zero, like a coiled spring that isn’t stretched at all.
When quarks are close together, the electrical force takes over, which often leads to a mutual repulsion.
But when the color-charged objects are far apart, the strong force gets stronger. Like a stretched spring, it works to pull the quarks back together.
Based on the magnitude of the color charges and the strength of the strong force, along with the electric charges of each of the quarks, that’s how we arrive at the size of the proton and the neutron: where the strong and electromagnetic forces roughly balance.
APS/Alan Stonebraker
The three valence quarks of a proton contribute to its spin, but so do the gluons, sea quarks and antiquarks, and orbital angular momentum as well. The electrostatic repulsion and the attractive strong nuclear force, in tandem, are what give the proton its size.
On slightly larger scales, the strong force holds protons and neutrons together in an atomic nucleus, overcoming the electrostatic repulsion between the individual protons. This nuclear force is a residual effect of the strong nuclear force, which only works over very short distances.
Because individual protons and neutrons themselves are color-neutral, the exchange is mediated by virtual, unstable particles known as pions, which explains why nuclei beyond a certain size become unstable; it’s too difficult for pions to be exchanged across larger distances. Only in the case of neutron stars does the addition of gravitational binding energy suppress the nucleus’ tendency to rearrange itself into a more stable configuration.
Wikimedia Commons user Manishearth
And on the scale of the atom itself, the key is that the lowest-energy configuration of any electron bound to a nucleus isn’t a zero-energy state, but is actually a relatively high-energy one compared to the electron’s rest mass.
This quantum configuration means that the electron itself needs to zip around at very high speeds inside the atom; even though the nucleus and the electron are oppositely charged, the electron won’t simply hit the nucleus and remain at the center.
Instead, the electron exists in a cloud-like configuration, zipping and swirling around the nucleus (and passing through it) at a distance that’s almost a million times as great as the size of the nucleus itself.
The energy levels and electron wavefunctions that correspond to different states within a hydrogen atom, although the configurations are extremely similar for all atoms. The energy levels are quantized in multiples of Planck’s constant, but the sizes of the orbitals and atoms are determined by the ground-state energy and the electron’s mass.
There are some fun caveats that allow us to explore how these sizes change in extreme conditions. In extremely massive planets, the atoms themselves begin to get compressed due to large gravitational forces, meaning you can pack more of them into a small space.
Jupiter, for example, has three times the mass of Saturn, but is only about 20% larger in size. If you replace an electron in a hydrogen atom with a muon, an unstable electron-like particle that has the same charge but 206 times the mass, the muonic hydrogen atom will be only 1/206th the size of normal hydrogen.
And a Uranium atom is actually larger in size than the individual protons-and-neutrons would be if you packed them together, due to the long-range nature of the electrostatic repulsion of the protons, compared to the short-range nature of the strong force.
Image credit: Calvin Hamilton.
The planets of the Solar System, shown to the scale of their physical sizes, show a Saturn that’s almost as large as Jupiter. However, Jupiter is 3 times as massive, indicating that its atoms are substantially compressed due to gravitational pressure.
By having different forces at play of different strengths, you can build a proton, neutron, or other hadron of finite size out of point-like quarks. By combining protons and neutrons, you can build nuclei of larger sizes than their individual components, bound together, would give you. And by binding electrons to the nucleus, you can build a much larger structure, all owing to the fact that the zero-point energy of an electron bound to an atom is much greater than zero.
In order to get a Universe filled with structures that take up a finite amount of space and have a non-zero size, you don’t need anything more than zero-dimensional, point-like building blocks. Forces, energy, and the quantum properties inherent to particles themselves are more than enough to do the job.
__________________________________________
Ethan Siegel is the founder and primary writer of Starts With A Bang!
This website is educational. Materials within it are being used in accord with the Fair Use doctrine, as defined by United States law.
§107. Limitations on Exclusive Rights: Fair Use
Notwithstanding the provisions of section 106, the fair use of a copyrighted work, including such use by reproduction in copies or phone records or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use, the factors to be considered shall include:
the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;
the nature of the copyrighted work;
the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
the effect of the use upon the potential market for or value of the copyrighted work. (added pub. l 94-553, Title I, 101, Oct 19, 1976, 90 Stat 2546)
Organelles
A car is a working machine – made from smaller systems working together.
A cell is an organic, living machine – made from organelles working together.
No part of a car, by itself, is functioning.
No part of a cell, by itself, is alive.
What we a “functioning car” is the way that parts work together.
What we call “life” is the way that organelles work together.
Let’s compare the parts of a car with the parts of a cell
Consider: The transmission, the axles and the engine.
Yet disconnect just one of these systems, and we effectively no longer have a car.
We’d just have an inert 2000 pound block of metal and plastic.
A car is not a car unless the parts are connected and working together.
The same is true for cells.
Inside the engine, what would happen if we removed or froze the pistons?
We’d effectively no longer have an engine.
The same is true for organelles inside cells.
Similarly, consider the ways that organelles and organic molecules are interacting within our cells.
This is mitochondrial ATP synthase. See how it is just like a machine? This is a machine with organic parts.
All parts of the body, when examined in detail, turn out to work in the same way: Like a simple machine, with parts that move against other parts, and objects that move from one place to another.
Nucleus to ribosomes to ER GIF from NPR: Protein synthesis
What would happen if we removed some of these parts?
We’d effectively no longer have a living cell.
You’ve seen parts inside cars. Now let’s look at the organelles (parts inside cells)
First, a note of caution about artwork: Many books simplify what a cell looks like, with a 2D black & white drawing, like this. This picture is “true” – but simplified.
In reality cells are 3D.
Organelles are suspended in cytoplasm throughout the cell.
Now let’s learn the job of each organelle using analogies:
Organelle |
Function |
Analogy |
|---|---|---|
lipid bilayer |
Controls which molecules go in/out of the cell |
Walls and doors |
cytoplasm |
Suspends and holds all the organelles |
the factory floor, where all the work is done. |
nucleus |
Chromosome (DNA) storage |
Control center |
chromosomes(made of DNA) |
Instructions for building and running the cell |
blueprints and instructions |
mitochondrion |
Converts energy from food molecules into a form usable by the cell |
Powerhouse |
ribosomes |
biological protein synthesis (translation) |
Workers on the assembly line, building our product. |
cytoskeleton |
gives the cell its shape and mechanical resistance to deformation |
Walls & studs, support and structure |
golgi body |
Packages proteins into vesicles inside the cell, and send them to their destination. |
Receives product from ER. Like UPS, its packages and distributes the products. |
endoplasmic reticulum(ER) |
Manufactures lipids and proteins |
Assembly line which makes our products |
lysosome |
Contain enzymes that can break down virtually all kinds of biomolecules. |
garbage disposal |
vacuoles |
Multiple uses, often related to storing molecules. |
Storage |
Organelles unique to plants
Click here to read about the organelles in more depth.
Endomembrane system
More details here: The endomembrane system
Endomembrane system by Mariana Ruiz Villarreal, LadyofHats
Learning Standards
2016 Massachusetts Science and Technology/Engineering Curriculum Framework
6.MS-LS1-2. Develop and use a model to describe how parts of cells contribute to the cellular functions of obtaining food, water, and other nutrients from its environment,
disposing of wastes, and providing energy for cellular processes.
2006 Massachusetts Science and Technology/Engineering Curriculum Framework
Biology High School Standards: Cells have specific structures and functions that make them distinctive. Processes in a cell can be classified broadly as growth, maintenance, and reproduction.
2.1 Relate cell parts/organelles (plasma membrane, nuclear envelope, nucleus, nucleolus, cytoplasm, mitochondrion, endoplasmic reticulum, Golgi apparatus, lysosome, ribosome, vacuole, cell wall, chloroplast, cytoskeleton, centriole, cilium, flagellum, pseudopod) to their functions. Explain the role of cell membranes as a highly selective barrier (diffusion, osmosis, facilitated diffusion, active transport).
Benchmarks for Science Literacy, AAAS
By the end of the 12th grade, students should know that
- Every cell is covered by a membrane that controls what can enter and leave the cell. 5C/H1a
- In all but quite primitive cells, a complex network of proteins provides organization and shape and, for animal cells, movement. 5C/H1b
- Within the cells are specialized parts for the transport of materials, energy capture and release, protein building, waste disposal, passing information, and even movement. 5C/H2a
Cellular and molecular biology: Cell structure and organization, mitosis, photosynthesis, cellular respiration, enzymes, biosynthesis, biological chemistry
External links
XKCD: Although the climate has always changed, that is no comfort
Yes, the climate has always changed. This shows why that’s no comfort.
By Brad Plumer, vox.com Jan 13, 2017
Randall Munroe, the author of the webcomic XKCD, has a habit of making wonderfully lucid infographics on otherwise difficult scientific topics. Everyone should check his take on global warming. It’s a stunning graphic showing Earth’s recent climate history. Take some time with it. Stroll through the events like the domestication of dogs and the construction of Stonehenge. And then ponder the upshot here.
There’s a common line among climate skeptics that “[t]he climate has always changed, so why worry if it’s changing now?” The first half of that sentence is undeniably true. Due to orbital wobbles, volcanic activity, rock weathering, and changes in solar activity, the Earth’s temperature has waxed and waned over the past 4.5 billion years. During the Paleocene it was so warm that crocodiles swam above the Arctic Circle. And 20,000 years ago it was cold enough that multi-kilometer-thick glaciers covered Montreal.
But Munroe’s comic below hits at the “why worry.” What’s most relevant to us humans, living in the present day, is that the climate has been remarkably stable for the past 12,000 years. That period encompasses all of human civilization — from the pyramids to the Industrial Revolution to Facebook and beyond. We’ve benefited greatly from that stability. It’s allowed us to build farms and coastal cities and thrive without worrying about overly wild fluctuations in the climate.
And now we’re losing that stable climate. Thanks to the burning of fossil fuels and land use changes, the Earth is heating up at the fastest rate in millions of years, a pace that could prove difficult to adapt to. Sea level rise, heat waves, droughts, and floods threaten to make many of our habitats and infrastructure obsolete. Given that, it’s hardly a comfort to know that things were much, much hotter when dinosaurs roamed the Earth.
Image by XKCD (Randall Munroe)
Articles
Global warming and greenhouse gases
Global warming has not stopped
Global warming: Pause in the rate of temp rise
Global warming Industry knew of climate change
Global warming: Adjusted data sets are a normal part of science
Climate skeptics are not like Galileo.
Yes, the climate has always changed. But this shows why that’s no comfort: XKCD infographic
Radar
Radar was developed secretly for military use by several nations, before and during World War II.The term was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging. It entered English and other languages as a common noun, losing all capitalization.
Radar uses radio waves to determine the range, angle, or velocity of objects.
*
*
EM waves can be of many different wavelengths.
Longer wavelengths we perceive as orange and red
Shorter wavelengths are towards the blue end of the spectrum
Fields are at right-angles to each other
They travel through vacuum (empty space) at the speed of light
c = speed of light
c = 3 x 108 m/s = 186,282 miles/second
So all parts of the EM spectrum – radio, light, Wi-Fi, X-rays,
are all made of exactly the same thing! The only thing different among them? wavelength and frequency!
Our eyes can only see a tiny amount of the EM spectrum.
There are longer and shorter waves as well.
Is used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain.
A radar system consists of:
transmitter producing electromagnetic radio waves
a receiving antenna (often the same antenna is used for transmitting and receiving)
a receiver and processor to determine properties of the object(s)
Radio waves from the transmitter reflect off the object and return to the receiver
This gives info about the object’s location and speed.
Uses
air and terrestrial traffic control
radar astronomy
air-defence systems / antimissile systems
tba
marine radars to locate landmarks and other ships
aircraft anticollision systems
outer space surveillance and rendezvous systems
meteorological (weather) precipitation monitoring
flight control systems
guided missile target locating systems
ground-penetrating radar for geological observation
Learning Standards
2016 Massachusetts Science and Technology/Engineering Curriculum Framework
6.MS-PS4-1. Use diagrams of a simple wave to explain that (a) a wave has a repeating pattern with a specific amplitude, frequency, and wavelength, and (b) the amplitude of a wave is related to the energy of the wave.
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-PS4-5. Communicate technical information about how some technological devices use the principles of wave behavior and wave interactions with matter to transmit and capture information and energy. Clarification Statements:
• Emphasis is on qualitative information and descriptions.
• Examples of technological devices could include solar cells capturing light and
converting it to electricity, medical imaging, and communications technology.
Massachusetts Science and Technology/Engineering Curriculum Framework (2006)
6. Electromagnetic Radiation Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum. 6.1 Recognize that electromagnetic waves are transverse waves and travel at the speed of light through a vacuum. 6.2 Describe the electromagnetic spectrum in terms of frequency and wavelength, and identify the locations of radio waves, microwaves, infrared radiation, visible light (red, orange, yellow, green, blue, indigo, and violet), ultraviolet rays, x-rays, and gamma rays on the spectrum.
Astronomy Learning Standards
Learning standards for astronomy, and related parts of Earth Science.
Massachusetts Curriculum Frameworks Science and Technology/Engineering (2016)
6.MS-ESS1-1a. Develop and use a model of the Earth-Sun-Moon system to explain the causes of lunar phases and eclipses of the Sun and Moon.
6.MS-ESS1-5(MA). Use graphical displays to illustrate that Earth and its solar system are one of many in the Milky Way galaxy, which is one of billions of galaxies in the universe.
8.MS-ESS1-1b. Develop and use a model of the Earth-Sun system to explain the cyclical pattern of seasons, which includes Earth’s tilt and differential intensity of sunlight on
different areas of Earth across the year
8.MS-ESS1-2. Explain the role of gravity in ocean tides, the orbital motions of planets, their moons, and asteroids in the solar system
HS-ESS1-1. Use informational text to explain that the life span of the Sun over approximately 10 billion years is a function of nuclear fusion in its core. Communicate that stars, through nuclear fusion over their life cycle, produce elements from helium to iron and release energy that eventually reaches Earth in the form of radiation.
HS-ESS1-2. Describe the astronomical evidence for the Big Bang theory, including the red shift of light from the motion of distant galaxies as an indication that the universe is currently expanding, the cosmic microwave background as the remnant radiation from the Big Bang, and the observed composition of ordinary matter of the universe, primarily found in stars and interstellar gases, which matches that predicted by the Big Bang theory (3/4 hydrogen and 1/4 helium).
HS-ESS1-4. Use Kepler’s laws to predict the motion of orbiting objects in the solar system.
Describe how orbits may change due to the gravitational effects from, or collisions
with, other objects in the solar system. Kepler’s laws apply to human-made satellites as well as planets, moons, and other objects.
=============================
A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (2012)
Stars’ radiation of visible light and other forms of energy can be measured and studied to develop explanations about the formation, age, and composition of the universe. Stars go through a sequence of developmental stages—they are formed; evolve in size, mass, and brightness; and eventually burn out. Material from earlier stars that exploded as supernovas is recycled to form younger stars and their planetary systems. The sun is a medium-sized star about halfway through its predicted life span of about 10 billion years.
Grade Band Endpoints for ESS1.A
By the end of grade 2. Patterns of the motion of the sun, moon, and stars in the sky can be observed, described, and predicted. At night one can see the light coming from many stars with the naked eye, but telescopes make it possible to see many more and to observe them and the moon and planets in greater detail.
By the end of grade 5. The sun is a star that appears larger and brighter than other stars because it is closer. Stars range greatly in their size and distance from Earth.
By the end of grade 8. Patterns of the apparent motion of the sun, the moon, and stars in the sky can be observed, described, predicted, and explained with models. The universe began with a period of extreme and rapid expansion known as the Big Bang. Earth and its solar system are part of the Milky Way galaxy, which is one of many galaxies in the universe.
By the end of grade 12. The star called the sun is changing and will burn out over a life span of approximately 10 billion years. The sun is just one of more than 200 billion stars in the Milky Way galaxy, and the Milky Way is just one of hundreds of billions of galaxies in the universe. The study of stars’ light spectra and brightness is used to identify compositional elements of stars, their movements, and their distances from Earth.
Grade Band Endpoints for ESS1.B
By the end of grade 2. Seasonal patterns of sunrise and sunset can be observed, described, and predicted.
By the end of grade 5. The orbits of Earth around the sun and of the moon around Earth, together with the rotation of Earth about an axis between its North and South poles, cause observable patterns. These include day and night; daily and seasonal changes in the length and direction of shadows; phases of the moon; and different positions of the sun, moon, and stars at different times of the day, month, and year.
Some objects in the solar system can be seen with the naked eye. Planets in the night sky change positions and are not always visible from Earth as they orbit the sun. Stars appear in patterns called constellations, which can be used for navigation and appear to move together across the sky because of Earth’s rotation.
By the end of grade 8. The solar system consists of the sun and a collection of objects, including planets, their moons, and asteroids that are held in orbit around the sun by its gravitational pull on them. This model of the solar system can explain tides, eclipses of the sun and the moon, and the motion of the planets in the sky relative to the stars. Earth’s spin axis is fixed in direction over the short term but tilted relative to its orbit around the sun. The seasons are a result of that tilt and are caused by the differential intensity of sunlight on different areas of Earth across the year.
By the end of grade 12. Kepler’s laws describe common features of the motions of orbiting objects, including their elliptical paths around the sun. Orbits may change due to the gravitational effects from, or collisions with, other objects in the solar system. Cyclical changes in the shape of Earth’s orbit around the sun, together with changes in the orientation of the planet’s axis of rotation, both occurring over tens to hundreds of thousands of years, have altered the intensity and distribution of sunlight falling on Earth. These phenomena cause cycles of ice ages and other gradual climate changes.
Earth exchanges mass and energy with the rest of the solar system. It gains or loses energy through incoming solar radiation, thermal radiation to space, and gravitational forces exerted by the sun, moon, and planets. Earth gains mass from the impacts of meteoroids and comets and loses mass from the escape of gases into space. (p.180)
=============================
NGSS
MS-ESS1-1. Develop and use a model of the Earth-sun-moon system to describe the cyclic patterns of lunar phases,
eclipses of the sun and moon, and seasons. [Clarification Statement: Examples of models can be physical, graphical, or conceptual.]
MS-ESS1-2. Develop and use a model to describe the role of gravity in the motions within galaxies and the solar system.
[Clarification Statement: Emphasis for the model is on gravity as the force that holds together the solar system and Milky Way galaxy and controls orbital motions
within them. Examples of models can be physical (such as the analogy of distance along a football field or computer visualizations of elliptical orbits) or conceptual (such as mathematical proportions relative to the size of familiar objects such as students’ school or state).]
MS-ESS1-3. Analyze and interpret data to determine scale properties of objects in the solar system. [Clarification Statement: Emphasis is on the analysis of data from Earth-based instruments, space-based telescopes, and spacecraft to determine similarities and differences among solar system objects. Examples of scale properties include the sizes of an object’s layers (such as crust and atmosphere), surface features (such as volcanoes), and orbital radius. Examples of data include statistical information, drawings and photographs, and models.]
MS-ESS1-4. Construct a scientific explanation based on evidence
ESS1.A: The Universe and Its Stars
Patterns of the apparent motion of the sun, the moon, and stars in
the sky can be observed, described, predicted, and explained with
models. (MS-ESS1-1)
Earth and its solar system are part of the Milky Way galaxy, which is
one of many galaxies in the universe. (MS-ESS1-2)
ESS1.B: Earth and the Solar System
The solar system consists of the sun and a collection of objects,
including planets, their moons, and asteroids that are held in orbit
around the sun by its gravitational pull on them. (MS-ESS1-2),(MSESS1-3)
This model of the solar system can explain eclipses of the sun and
the moon. Earth’s spin axis is fixed in direction over the short-term
but tilted relative to its orbit around the sun. The seasons are a
result of that tilt and are caused by the differential intensity of
sunlight on different areas of Earth across the year. (MS-ESS1-1)
The solar system appears to have formed from a disk of dust and
gas, drawn together by gravity. (MS-ESS1-2)
Disciplinary Core Ideas ESS1.B: Earth and the Solar System
Cyclical changes in the shape of Earth’s orbit around the sun,
together with changes in the tilt of the planet’s axis of rotation,
both occurring over hundreds of thousands of years, have altered
the intensity and distribution of sunlight falling on the earth.
These phenomena cause a cycle of ice ages and other gradual
climate changes.
=============================
Benchmarks: American Association for the Advancement of Science
By the end of the 8th grade, students should know that
Because every object is moving relative to some other object, no object has a unique claim to be at rest. Therefore, the idea of absolute motion or rest is misleading. 10A/M1*
Telescopes reveal that there are many more stars in the night sky than are evident to the unaided eye, the surface of the moon has many craters and mountains, the sun has dark spots, and Jupiter and some other planets have their own moons. 10A/M2
By the end of the 12th grade, students should know that
To someone standing on the earth, it seems as if it is large and stationary and that all other objects in the sky orbit around it. That perception was the basis for theories of how the universe is organized that prevailed for over 2,000 years. 10A/H1*
Ptolemy, an Egyptian astronomer living in the second century A.D., devised a powerful mathematical model of the universe based on continuous motion in perfect circles, and in circles on circles. With the model, he was able to predict the motions of the sun, moon, and stars, and even of the irregular “wandering stars” now called planets. 10A/H2*
In the 1500s, a Polish astronomer named Copernicus suggested that all those same motions could be explained by imagining that the earth was turning around once a day and orbiting around the sun once a year. This explanation was rejected by nearly everyone because it violated common sense and required the universe to be unbelievably large. Worse, it flew in the face of the belief, universally held at the time, that the earth was at the center of the universe. 10A/H3*
Johannes Kepler, a German astronomer, worked with Tycho Brahe for a short time. After Brahe’s death, Kepler used his data to show mathematically that Copernicus’ idea of a sun-centered system worked well if uniform circular motion was replaced with uneven (but predictable) motion along off-center ellipses. 10A/H4*
Using the newly invented telescope to study the sky, Galileo made many discoveries that supported the ideas of Copernicus. It was Galileo who found the moons of Jupiter, sunspots, craters and mountains on the moon, and many more stars than were visible to the unaided eye. 10A/H5
Writing in Italian rather than in Latin (the language of scholars at the time), Galileo presented arguments for and against the two main views of the universe in a way that favored the newer view. His descriptions of how things move provided an explanation for why people might notice the motion of the earth. Galileo’s writings made educated people of the time aware of these competing views and created political, religious, and scientific controversy. 10A/H6*
Tycho Brahe, a Danish astronomer, proposed a model of the universe that was popular for a while because it was somewhat of a compromise of Ptolemy’s and Copernicus’ models. Brahe made very precise measurements of the positions of the planets and stars in an attempt to validate his model. 10A/H7**
The work of Copernicus, Galileo, Brahe, and Kepler eventually changed people’s perception of their place in the universe. 10A/H8** (SFAA)
By the end of the 12th grade, students should know that
Isaac Newton, building on earlier descriptions of motion by Galileo, Kepler, and others, created a unified view of force and motion in which motion everywhere in the universe can be explained by the same few rules. Newton’s system was based on the concepts of mass, force, and acceleration; his three laws of motion relating them; and a physical law stating that the force of gravity between any two objects in the universe depends only upon their masses and the distance between them. 10B/H1*
Newton’s mathematical analysis of gravitational force and motion showed that planetary orbits had to be the very ellipses that Kepler had proposed two generations earlier. 10B/H2*
The Newtonian system made it possible to account for such diverse phenomena as tides, the orbits of planets and moons, the motion of falling objects, and the earth’s equatorial bulge. 10B/H3*
For several centuries, Newton’s science was accepted without major changes because it explained so many different phenomena, could be used to predict many physical events (such as the appearance of Halley’s comet), was mathematically sound, and had many practical applications. 10B/H4
Although overtaken in the 1900s by Einstein’s relativity theory, Newton’s ideas persist and are widely used. Moreover, his influence has extended far beyond physics and astronomy, serving as a model for other sciences and even raising philosophical questions about free will and the organization of social systems. 10B/H5*
By the end of the 12th grade, students should know that
Prior to the 1700s, many considered the earth to be just a few thousand years old. By the 1800s, scientists were starting to realize that the earth was much older even though they could not determine its exact age. 10D/H1*
In the early 1800s, Charles Lyell argued in Principles of Geology that the earth was vastly older than most people believed. He supported his claim with a wealth of observations of the patterns of rock layers in mountains and the locations of various kinds of fossils. 10D/H2*
In formulating and presenting his theory of biological evolution, British naturalist Charles Darwin adopted Lyell’s claims about the age of the earth and his assumption that the processes that occurred in the past are the same as the processes that occur today. 10D/H3*
By the end of the 5th grade, students should know that
The patterns of stars in the sky stay the same, although they appear to move across the sky nightly, and different stars can be seen in different seasons. 4A/E1
Telescopes magnify the appearance of some distant objects in the sky, including the moon and the planets. The number of stars that can be seen through telescopes is dramatically greater than can be seen by the unaided eye. 4A/E2
Planets change their positions against the background of stars. 4A/E3
The earth is one of several planets that orbit the sun, and the moon orbits around the earth. 4A/E4
Stars are like the sun, some being smaller and some larger, but so far away that they look like points of light. 4A/E5
A large light source at a great distance looks like a small light source that is much closer. 4A/E6** (BSL)
By the end of the 8th grade, students should know that
The sun is a medium-sized star located near the edge of a disc-shaped galaxy of stars, part of which can be seen as a glowing band of light that spans the sky on a very clear night. 4A/M1a
The universe contains many billions of galaxies, and each galaxy contains many billions of stars. To the naked eye, even the closest of these galaxies is no more than a dim, fuzzy spot. 4A/M1bc
The sun is many thousands of times closer to the earth than any other star. Light from the sun takes a few minutes to reach the earth, but light from the next nearest star takes a few years to arrive. The trip to that star would take the fastest rocket thousands of years. 4A/M2abc
Some distant galaxies are so far away that their light takes several billion years to reach the earth. People on earth, therefore, see them as they were that long ago in the past. 4A/M2de
Nine planets of very different size, composition, and surface features move around the sun in nearly circular orbits. Some planets have a variety of moons and even flat rings of rock and ice particles orbiting around them. Some of these planets and moons show evidence of geologic activity. The earth is orbited by one moon, many artificial satellites, and debris. 4A/M3
Many chunks of rock orbit the sun. Those that meet the earth glow and disintegrate from friction as they plunge through the atmosphere—and sometimes impact the ground. Other chunks of rock mixed with ice have long, off-center orbits that carry them close to the sun, where the sun’s radiation (of light and particles) boils off frozen materials from their surfaces and pushes it into a long, illuminated tail. 4A/M4*
By the end of the 12th grade, students should know that
The stars differ from each other in size, temperature, and age, but they appear to be made up of the same elements found on earth and behave according to the same physical principles. 4A/H1a
Unlike the sun, most stars are in systems of two or more stars orbiting around one another. 4A/H1b
On the basis of scientific evidence, the universe is estimated to be over ten billion years old. The current theory is that its entire contents expanded explosively from a hot, dense, chaotic mass. 4A/H2ab
Stars condensed by gravity out of clouds of molecules of the lightest elements until nuclear fusion of the light elements into heavier ones began to occur. Fusion released great amounts of energy over millions of years. 4A/H2cd
Eventually, some stars exploded, producing clouds containing heavy elements from which other stars and planets orbiting them could later condense. The process of star formation and destruction continues. 4A/H2ef
Increasingly sophisticated technology is used to learn about the universe. Visual, radio, and X-ray telescopes collect information from across the entire spectrum of electromagnetic waves; computers handle data and complicated computations to interpret them; space probes send back data and materials from remote parts of the solar system; and accelerators give subatomic particles energies that simulate conditions in the stars and in the early history of the universe before stars formed. 4A/H3
Mathematical models and computer simulations are used in studying evidence from many sources in order to form a scientific account of the universe. 4A/H4
As the earth and other planets formed, the heavier elements fell to their centers. On planets close to the sun (Mercury, Venus, Earth, and Mars), the lightest elements were mostly blown or boiled away by radiation from the newly formed sun; on the outer planets (Jupiter, Saturn, Uranus, Neptune, and Pluto) the lighter elements still surround them as deep atmospheres of gas or as frozen solid layers. 4A/H5** (SFAA)
Our solar system coalesced out of a giant cloud of gas and debris left in the wake of exploding stars about five billion years ago. Everything in and on the earth, including living organisms, is made of this material. 4A/H6** (SFAA)
Can we stop a hurricane
Can we stop a hurricane? Sounds like something out of science fiction, a proposal fitting of mad scientists, right?
Remember Hurricane Katrina? August 2005. It was a destructive Category 5 Atlantic hurricane that caused over 1,800 fatalities and $125 billion in damage. Damaged the are of and around the city of New Orleans. What if there had been a way to shift its course, or reduce its intensity?
In Hurricane Forcing: Can Tropical Cyclones Be Stopped? by Christopher Mims, Scientific American, October 23, 2009, we read
This past June, a plan to reduce the severity and frequency of hurricanes leaked to the public in the form of a patent application under Bill Gates’s name (along with many others), resuscitating speculation about a scheme that has been proposed off and on since the 1960s. The core of the idea remains the same: mixing the warm surface waters that fuel tropical cyclones with cooler waters below to drain storms of their energy. But now Stephen Salter an emeritus professor of engineering design at the University of Edinburgh proposes a new—and possibly more realistic—method of mixing.
Salter has outlined in an engineering paper the design for a floating structure 100 meters in diameter—basically a circular raft of lashed-together used tires (to reduce cost). It would support a thin plastic tube 100 meters in diameter and 200 meters in length.
When deployed in the open ocean, the tube would hang vertically, descending through the warm, well-mixed upper reaches of the ocean and terminating in a deeper part of the water column known as the thermocline, where water temperatures drop precipitously.
The point of this design is to transfer warm surface water into the deeper, cooler reaches of the ocean, mixing the two together and, hopefully, cooling the sea surface. Salter’s design is relatively simple, using a minimum of material in order to make the construction of each of his devices cheap (millions of used tires are thrown away each year, worldwide); his scheme would also require the deployment of hundreds of these devices.
Using horizontal wave action at the ocean surface, passive no-return valves would capture energy by closing after a wave has passed through them, allowing the circular interior of each device to raise the level of the seawater within the device by, on average, 20 centimeters. The weight of the gathered warm water would thereby create downward pressure, pushing it down the tube.
The idea is that hundreds of these floating wave-powered seawater pumps would be deployed year-round in areas, such as the eastern tropical Atlantic and the Gulf of Mexico, where hurricanes typically spawn or grow in intensity. (The devices would not, as widely speculated, be deployed only in the path of a hurricane that already formed.) …
In Can Science Halt Hurricanes? we read
Until recently, the U.S. Department of Homeland Security has been investigating whether seeding storm clouds with pollution-size aerosols (particles suspended in gas) might help slow tropical cyclones. Computer models suggest that deploying aerosols can have “an appreciable impact on tropical cyclone intensity,” writes William Cotton, an atmospheric scientist at Colorado State University. He and his colleagues recently reviewed such work in the Journal of Weather Modification. In fact, human pollution may already be weakening storms, including August’s Hurricane Irene. “[Computer] models all predicted that the intensity of Irene would be much greater than it was,” Cotton notes. “Was that because they did not include aerosol effects?”…
In The Insider, Kelley Dickerson writes
Engineers could stop hurricanes with the ‘sunglasses effect’ — but it’d require a huge sacrifice
According to new research published in the journal Proceedings of the National Academy of Sciences, if we pumped sulfate gases into our planet’s upper atmosphere, we could cool down our oceans enough to cut the number of Katrina-force hurricanes in half over the next 50 years. It’d require about 10 billion tons of sulfates to get the job done, which is tens or hundreds of times the sulfates a typical volcanic eruption can form.
From Stanford University we read
Computer simulations by Professor Mark Z. Jacobson have shown that offshore wind farms with thousands of wind turbines could have sapped the power of three real-life hurricanes, significantly decreasing their winds and accompanying storm surge, and possibly preventing billions of dollars in damages…. he found that the wind turbines could disrupt a hurricane enough to reduce peak wind speeds by up to 92 mph and decrease storm surge by up to 79 percent.
The study, conducted by Jacobson, and Cristina Archer and Willett Kempton of the University of Delaware, was published online in Nature Climate Change….
Taming Hurricanes With Arrays of Offshore Wind Turbines (Nature Climate Change, 2014)
In this intriguing discussion, science fiction writers look into the real physics of the question, What would be need to stop a hurricane? What would we need to stop a hurricane? Worldbuilding @ Stackexchange
Also see these great topics at Hurricane Research Division NOAA, National Oceanic and Atmospheric Administration
Tropical Cyclone Modification and Myths
Tier I, II and III vocabulary
What are the critical words in our lessons? These include not only new terms that we introduce in that topic, but more importantly, all of the common words that students supposedly “already know.” The problem is that many students don’t always know what these words means.
Tier One – These are everyday words – including nouns, verbs, adverbs, and adjectives – that are learned in the early grades. By the time we get to high school classes, teachers shouldn’t even need to think about teaching such vocabulary.
Tier Two – Here we go! These are high frequency words, used across content areas, that are key to a student understanding directions, understanding relationships, and for making inferences.
The problem with tier two words is that although all students read and use them, some don’t fully understand how they function.
High school teachers thus need to carefully examine student reading and verbal comprehension early on in the year, and take care to explain and model how these terms are used.
Academic language from resources.successforall.org
Tier Three – These are low-frequency, domain-specific words. These words only come up in certain subjects, or certain topics.
External resources
Worksheet: Three Tiers of Vocabulary and Education
Latest Posts
-
Importance of art education
Why is teaching art intrinsically important to being human? Some would have us believe that we should have art education in our schools because it…
-
What are broken symmetries?
Symmetry is an important concept for understanding how our universe works. Symmetry lets us see what stays the same when certain conditions change. Symmetries are…
-
Native Americans in New England
When did the ancestors of native Americans arrive in what we now call New England? Their earliest confirmed presence in New England is about 12,000–13,000…
-
Why is music education important
Why is music intrinsically important to being human? Every year I read yet another article trying to persuade us that we should have music education…
KaiserScience 