Centripetal force is fun to experiment with. It is the same force that makes a playground swing move and the moon orbit the Earth. I always thought it seemed to defy gravity – an amazing feat. Let’s try a simple, fun activity to demonstrate centripetal force and amaze your friends. Then, we will learn more about centripetal force and see how it really works.
Centripetal Force Experiment
- a glass jar or pitcher
- a marble
Place the marble in the jar or pitcher.
Place the palm of your hand over the opening of the jar with the marble inside. Turn the jar or pitcher on its side.
Move the jar in circles until the marble spins around the inside of the jar. Continue spinning the marble and slowly turn the jar upside down with your hand still over the mouth of the jar. The marble should still be spinning around the inside of the jar. The key is to keep the jar moving a constant speed so that the speed of the marble is also constant.
Centripetal Force Explained
A force is a push or a pull on an object. It can cause the object to gain speed, slow down, stay in one place, or even change shape. Forces are in action all around us. You use force to throw a ball up into the air and the force of gravity pulls it back down.
When we think about a force acting on an object, we usually think of that object moving in a straight line. Sometimes a force moves an object in a circle. This force is called centripetal force. Centripetal force causes an object to move in a curved line because it is being pulled toward a center point.
In the case of the marble in the jar, the jar pushes on the marble and provides the inward force that keeps the marble moving in a circular path. If the bottle were suddenly removed, the centripetal force would be gone and the marble would fly off in a straight line because of its forward speed.
All objects that move in a circular path have a forward speed and a centripetal force pulling them inward. The moon and satellites that orbit the Earth are pulled toward the Earth by gravity. It is their own forward speed that keeps them from being pulled to the Earth. If their forward speed decreases, they will fall to Earth just like the marble when the jar stops moving.