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# Tides

Beach in the UK

## Cause of tides on both sides

### Since the tides are caused by the Moon’s gravity pulling on Earth’s oceans, you might think the shape of the oceans would only be pulled toward the Moon.

Wiley.com Textbook animations for tides

## Spring and Neap Tides

http://www.astronomyknowhow.com/moon-tides.htm

### So the overall effect on the water is less, so the high tides are lower than average and the low tides are higher than the average.

Spring and Neap Tides Animation
http://oceanservice.noaa.gov/education/kits/tides/media/supp_tide06a.html

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Consider an object near the surface of the Earth. We assume Earth’s gravity acts equally on all parts of the object – the object’s top and bottom. For all practical purposes, this is true enough.

But it is not precisely true. The Earth’s gravity really acts on the bottom part of a falling object more than the top part. The bottom part is slightly closer to the center of the Earth.

Why don’t we notice this? Why don’t we feel the Earth tug on our feet more than on our head? The difference in height between the center of the Earth and the top of the object, and the bottom of the object, is slight. It is so tiny that it makes no measurable difference

But now consider a large object, like an asteroid or small moon. These can be tens, or hundreds, of miles in diameter. In this case, the difference in height between the center of the Earth and the top of the object, and the bottom of the object, is not so slight. It is large enough that it does make a measurable difference!

Now consider an object the size of the Earth being pulled by the moon’s gravity.

The diameter of the earth at the equator is 7,920 miles (12,760 kilometers)

Here, the difference in height between the center of the Moon and the near part of Earth, and the center of the Moon and the far part of Earth, is large. Since the Earth has water over most of its surface, we can easily see the result of this difference in gravitational force. A difference in gravitational force is called a “tidal force”.

Applets on Tides from the PBS NOVA website

What causes the tides?

Tidal curiosities – Questions & Answers

## The cause of the tides

By William Newtspeare http://squishtheory.wordpress.com/the-tides/

## The Bay of Fundy

### The Bay of Fundy is a bay on the Atlantic coast, on the northeast end of the Gulf of Maine, between the Canadian provinces of New Brunswick and Nova Scotia. It has highest tidal range in the world.

http://en.wikipedia.org/wiki/Bay_of_Fundy

http://bayoffundytourism.com/ecozones/worlds-highest-tides/

## More than 2 tides a day?

http://www.astronomyknowhow.com/moon-tides.htm

### The highest tides of all (17m) occur in Canada and after a long running dispute between the famous tides of the Bay of Fundy and those of Ungava Bay on the northern coast of Quebec, the Canadian Hydrographic Service has declared a draw.

Why Is There a Tidal Bulge Opposite the Moon? Stephen J Edberg, Jet Propulsion Laboratory, California Institute of Technology

https://pumas.gsfc.nasa.gov/files/01_25_11_1.pdf

Tidal Misconceptions, by Donald E. Simanek

http://www.lhup.edu/~dsimanek/scenario/tides.htm

AP Physics resources on tidal forces

An overview of oceanic tides (AP Physics only)

## Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

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-ESS1-4. 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.

HS-PS2-4. Use mathematical representations of Newton’s law of gravitation and Coulomb’s law to both qualitatively and quantitatively describe and pre

HS-PS2-10(MA). Use free-body force diagrams, algebraic expressions, and Newton’s laws of motion to predict changes to velocity and acceleration for an object moving in one
dimension in various situations.

A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (2012)

PS2.B: TYPES OF INTERACTIONS

Gravitational, electric, and magnetic forces between a pair of objects do not require that they be in contact. These forces are explained by force fields that contain energy and can transfer energy through space. These fields can be mapped by their effect on a test object (mass, charge, or magnet, respectively). Objects with mass are sources of gravitational fields and are affected by the gravitational fields of all other objects with mass. Gravitational forces are always attractive. For two human-scale objects, these forces are too small to observe without sensitive instrumentation. Gravitational interactions are non-negligible, however, when very massive objects are involved. Thus the gravitational force due to Earth, acting on an object near Earth’s surface, pulls that object toward the planet’s center. Newton’s law of universal gravitation provides the mathematical model to describe and predict the effects of gravitational forces between distant objects. These long-range gravitational interactions govern the evolution and maintenance of large-scale structures in the universe (e.g., the solar system, galaxies) and the patterns of motion within them… Newton’s law of universal gravitation and Coulomb’s law provide the mathematical models to describe and predict the effects of gravitational and electrostatic forces between distant objects.