Shop Windows to the Universe

We now offer the Cool It! card game in our Science Store. Cool It! is the new card game from UCS that teaches kids about the choices we have when it comes to climate change.
This image shows the Earth and the moon, and the bulges produced on each side from the tides.
Click on image for full size

Tidal Forces

The force of gravity caused by an object gets weaker as you move farther away from that object. In this picture, the Earth is pulling on the Moon, and the Moon is pulling on the Earth. The Moon pulls more strongly on the side of the Earth facing the Moon than on the side facing away from the Moon. Because the gravitational force on one side of the planet is different from that on the other side, it is called a tidal force.

Because planets are not perfectly rigid, they deform when subjected to such tidal forces (Earth also bulges at the equator all the way around because it is spinning). They deform as if they are being pushed from the top and bottom, and a bulge forms on either side of the planet. These two bulges are called tides. On Earth, near the ocean, these tides can actually be seen. The ocean water rises high along the beach, twice each day.

If a body is very rigid or is not held together well, instead of getting pushed and pulled out of shape, the tidal forces can actually tear the body in half, as with comet Shoemaker-Levy 9.

Last modified September 29, 2003 by Randy Russell.

Shop Windows to the Universe Science Store!

Our online store includes books on science education, classroom activities in The Earth Scientist, mineral and fossil specimens, and educational games!

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Cool It! Game

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

What is the distance from the Earth to the Sun when the Earth is at perihelion and when it is at aphelion? At what month is the Earth closest to the Sun? What is the circumference of the Earth? How fast is the Earth moving about its axis; how about around the Sun?

If a body (like the Earth) is orbiting around the Sun, we say it is closest to the Sun at perihelion and farthest from the Sun at aphelion. In 2000, perihelion for the Earth was on January 3, 2000, and...more

Tidewater

Have you ever walked along a beach at low tide? Everyone likes to look for uncovered sea shells or the small creatures in leftover puddles of water during low tide. One thing is for sure, low tide can...more

Evolution of Callisto

The insides of most of the moons and planets separated while they were forming out of the primitive solar nebula. Measurements by the Galileo spacecraft have been shown that Callisto is the same inside...more

Native American Astronomy

People from Asia crossed the Bering Strait into North America. These people were first in this new land and so they are known as Native Americans. Over time, these people broke into tribes (as seen on...more

AU

AU stands for Astronomical Units. It is a useful way to measure the distances in interplanetary space. It is the distance between the Earth and the Sun, which is about 93 million miles. For reference,...more

The Spiral of the IMF

The solar wind is formed as the Sun's top layer blows off into space, carrying magnetic fields still attached to the Sun. Gusts form in the solar wind associated with violent events on the Sun. Particles...more

Spiral Path of Material

For a planet to be affected by a blob of material being ejected by the sun, the planet must be in the path of the blob, as shown in this picture. The Earth and its magnetosphere are shown in the bottom...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF