The Mind Museum: Gravity Exhibit

A balance between centripetal and centrifugal forces keeps the moon in orbit around our planet, and this exhibit shows a motorized model of the moon being spun around the earth. Viewers are allowed to tip that balance by being given control of the moon's speed (see the big red speed dials?). Too slow and the freely hung moon crashes into the earth. Too fast and the moon moves farther away, eventually "escaping" its orbit.

More about The Mind Museum here.