By Paul Doherty

Senior Staff Scientist

The Exploratorium

San Francisco, CA


Part 1

The Three Moons of Earth, scientists have recently discovered two more co-orbital partners of the earth in addition to the Moon: Cruithne a 5 km diameter asteroid in a horseshoe orbit, and 2002AA29, a 100 m diameter asteroid which orbits the earth over the poles.

Part 2

Gravitational interactions, an explanation of how a planetary gravity assist works using a tennis ball and a basketball. When a tennis ball is dropped on top of a basketball the resulting collision launches the tennis ball at high velocity. The same mechanics applies when a satellite encounters a planet and uses the resulting "collision" to gain speed.

Bouncing Balls

Gravity Assist

Part 3

Gravity Wells, many museums have large gravity wells in which balls can be rolled to illustrate orbital mechanics. Different shaped wells such as a straight sided funnel and a spherical bowl produce interesting orbital variations.

Gravity Well

Gravity Well Math Root

Stocking Force Visualization


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Scientific Explorations with Paul Doherty

© 2003

21 August 2003