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# Determine the Bouncing of Rubber Balls That are at Different Temperatures

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Author: Janice VanCleave

### What You Need to Know

Elasticity is the ability of a material to return to its original length, shape, or size immediately after a deforming force has been removed. A bond is an attractive force between atoms.

### How Does Elasticity Work?

Elastic materials are things that can be bent, stretched, or squeezed and then return to their original size or shape. For example, when you stretch a rubber band, it returns to its original shape when you release it. How elastic a material is depends on how much the atoms can be separated without breaking the bonds between them.

### What Does This Have to Do with How Temperature Affects a Ball's Bounce?

When a ball is dropped, gravity pulls it toward the ground. As the ball falls, its potential energy changes to kinetic energy (energy of motion). When the ball hits the ground, it stops, and its kinetic energy goes into deforming the ball. Some of the ball's molecules are stretched apart and some are squeezed together. This changes the ball's original round shape to a squashed shape.

The squashed ball has potential energy because the elastic material the ball is made of makes it regain its round shape. This is due to the energy transfer from potential energy to kinetic energy. Thus, a shape change from flat to round pushes the ball back up.

### Fun Fact

Rubber balls have been found that date as early as 1600 B.C. These balls were made from natural rubber mixed with different plant juices, including the sap from morning glories. Like today's modern rubber, these mixtures produce a bouncy substance, but it is not as temperature resistant.

### Real-Life Science Challenge

Natural rubber is plant sap, particularly from the tree Hevea brasiliensis. Natural rubber becomes soft and sticky when hot, and hard and brittle when cold, so it isn't very good for making things. Between 1830 and 1839, the American inventor Charles Goodyear (1800–1860) solved this problem. After many unsuccessful attempts at making rubber that was useful at a wide range of temperatures, he accidentally dropped a mixture of rubber and sulfur on a hot stove. Instead of melting, the mixture charred. He called this process vulcanization. Today synthetic rubber, called neoprene, is used to make tires, wet suits, seals and gaskets, hoses, and many other products.

### Experiment

Now, start experimenting by comparing the bounce of rubber balls that are at different temperatures.

Hints

• Balls that do not have to be inflated are best. This eliminates the variable of inflation.
• Balls can be cooled in a refrigerator or heated in sunlight.
(Caution: Do not heat balls by any other method.)
• Work out a way to measure the height of the ball's bounce.