Space missions . Solar System . Volcanoes 101 . Site map . When you whirl a ball around at the end of a string, centripetal force applied to the string keeps the ball moving in a circle.
Gravity can also do the job, as it does when the Earth holds the Moon in orbit.
The red ball exerts and equal and opposite force, called centrifugal force , on the string and on you. It's like taking a corner in your car a little too fast and ending up in the ditch. How Planets Orbit to learn more about these forces. E-mail us with general site comments or suggestions. Newsticker for your site Earth .