Centripetal Force

Have you ever thrown your spare change into a coin vortex like the one we used to have in the gift shop at ECHO? When you put a coin in this, the coin spins around and around until eventually it reaches the bottom and goes through the hole in the center. This coin is demonstrating centripetal force. While an object moves due to velocity, or it’s speed in a certain direction, centripetal force is the force that keeps the object moving in a circular path. It’s centripetal because the force is always being pulled towards the center of the circle. Since we live on Earth, objects are also going to have other forces acting on them, like friction and gravity. The penny makes its way to the hole because friction slows it down. If you were to observe this penny in space, it would just keep moving in a circle! But alas, you wouldn’t survive in space (well, without a space suit or access to the International Space Station), so you will have to experiment with centripetal force the best we can with this experiment that you can do right at home!

Materials: Wine glass or wide mouth glass, marble or small ball.

Directions: Put the marble inside the wine glass and spin the marble around. Now try putting your hand on the mouth of the glass and turning it upside down. Keep your hand on the mouth of the glass as you begin to spin the ball again. When the ball is moving inside the glass, remove your hand, but keep spinning, and watch centripetal force in action!

How It Works: While inside the glass, the marble is creating an outward “pushing” force against the glass. The glass is providing an inward “pushing” force that keeps the marble moving in a circular motion. Centripetal force will keep the ball following this curved path. However, gravity is still the superior force and when you stop spinning the glass or slow down, the ball will eventually fall out!

Want more? Research it! How do astronauts use Centrifuges to prepare for the centripetal force they’ll feel in space?