Centennial Museum gecko logo

Desert Diary
Physics/Falling Moon


Remember Chicken Little? "The sky is falling, the sky is falling!" Well, being a birdbrain, she didn't get it quite right. It's really the moon that's falling! Outrageous claim? Nope. Sir Isaac Newton realized this way back in the 17th century.

Let's think a bit. Drop an object from 16 feet up, and it will hit the ground in 1 second. Now throw that object horizontally from the same height—it too will take 1 second to reach ground, even though it may land 10 feet away. Its pathway is an arc formed by a combination of falling downward 16 feet and traveling horizontally 10 feet. If you throw the object many miles, though, it has to fall more than 16 feet, because the earth's surface curves away. Throw it hard enough, and the surface curves away at the same rate that the object falls, and the object never reaches ground.

And this is exactly what the moon does—its combination of horizontal speed and falling speed balance out so it's literally falling AROUND the earth.
pen and ink


Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.

Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.

Moon Image

The moon. Image by NASA.



Web Resources

Newton and the Moon.

The Earth/Moon system as seen from space—the Voyager photograph.