Bouncing Ball Physics: What is Elasticity? (page 2)

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Author: Erin Bjornsson
Topics: Third Grade, Physics


On average, the rubber bouncy ball will bounce the highest, followed by the ping pong ball. The marble will bounce the least high.


When all three balls are dropped from the same height, the rubber ball will bounce the highest because it has the greatest elasticity. When the rubber ball hits the ground it gets compressed, or squished, and because it is very elastic, it quickly returns to its original shape. When it does this, it pushes back on the ground shoots back up into the air.

The marble, which is the hardest out of the three balls, has the least elasticity, so it does not bounce as high. It doesn’t get squished when it lands, so it has a harder time changing its direction from down to up. The balls dropped from 75 centimeters will bounce higher than those dropped from 50 centimeters, and the balls in the 50 centimeter trials will bounce higher than those in the 25 centimeter trials. This is because the higher the starting height of the ball, the higher the ball’s potential energy. An object has potential energy because of its position. If an object is going to be dropped from high up in the air, it has lots of potential energy because the earth’s gravity has plenty of time to accelerate, or speed up, the ball when you let go of it—and the longer an object falls, the faster it gets. So what happens to potential energy when a ball is dropped? It turns into kinetic energy, or the energy an object has when it is moving. The faster an object moves, the higher its kinetic energy. Which object do you think has a higher kinetic energy: a car or an airplane?

Because gravity has the most time to do its job when the balls are dropped from 75 centimeters, these balls have the most kinetic energy by the time they hit the ground. When the ball hits the ground, all that kinetic energy has to go somewhere. A lot of it goes back into the ball, giving it more force to pop back up into the air—so the higher the potential energy, the higher the kinetic energy, and the higher the kinetic energy, the higher the bounce!

Further investigation:

To explore gravity and gravitational forces, get a stopwatch and time each ball from the time it is dropped until it hits the ground. Which ball hits first? Does weight matter? Does elasticity matter?

Result: All balls should take the same amount of time to reach the ground when dropped from the same height. Weight and elasticity do not matter.

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