Activity: Experiencing Centrifugal Force

To perform this activity, you will need a merry-go-round and a small, light-weight ball.

1.  Get onto the merry-go-round and hold on tight.  Have someone spin you very fast. 
    a)  How do you feel yourself being pulled? 
    b)  If you were to let go– which you certainly won’t do– which way do you think you would go? 
    c)  Try moving to the center of the merry-go-round, to a point mid-way between the center and the edge, and then the edge.  At which location do you experience the most “pull”?

2.  Now have the person spin you at a moderate rate while you hold the small ball. 

3.  Look for a landmark object, such as a tree.  The next time you come to the tree, let go of the ball.  Make sure you just let go, don’t throw it.     
    a)  Where does the ball end up? 
    b)  Did it go directly towards the tree?

Have you ever been on one of those amusement park rides that you stand up in while it spins around very fast?  If you have, it feels as if you are being thrown out against the side doesn’t it? 

It’s called centrifugal force, but it is not a force at all.  It is an effect you feel that results from the curved shape of the ride and the forward motion you have.  An object moving in a circle, acts as if it were experiencing an external force when in fact it is not.  Centrifugal force is dependent on the the object’s mass, rotation speed, and the distance from the center of rotation. 

If the walls of the amusement park ride were to suddenly disappear, which way would you go– straight back, or to the side?  Remember which way the ball went when you let go of it while spinning around.

Think of what happens to you when you are in a car that turns suddenly.  You are thrown up against the side of the car.  The reason is explained by understanding an insight from Galileo.  He said things like to keep going the same direction and the same speed.  It takes a force to change the direction or speed of something.  So when the car turns, your body wants to go straight, at least until it is pulled back by the seat belt or hits the side of the car!  Thus, it feels as if you are being thrown up against the side of the car, when in reality you are just going straight as before, while the car is turning.  To better understand this, imagine that the amusement park ride is a square box instead of a circle.   What would happen?  You can try it with a marble and a cardboard box.  Spin the box with the marble in it and watch what happens!

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