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# Bill Nye Demonstration: Happy and Unhappy Ball

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Author: Bill Nye
##### Description:

Just what is happening when a ball bounces? Every child has played with a super ball - check out the disappointment when one of the toys doesn't do what's expected.

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Tutorial

## Happy and Unhappy Super Balls

Things can look very similar, but does that make them the same? Hmmmm...

## How Does it Work?

Although the two balls have some similar physical properties, such as size, color, and density, they differ greatly in elasticity. The one which bounces demonstrates an almost perfect elastic collision with a hard surface. Very little of its kinetic energy is converted into heat in the collision. This ball is often referred to as a 'super ball'. The ball which does not bounce demonstrates an almost perfect inelastic collision. Most of the kinetic energy is converted into heat.

### Here are the specifics:

• The ball which bounces is made from polyneoprene, which has large chlorine groups to restrict rotation on every fourth carbon in the long chain. Numerous cross links between polymer chains restrict the slipping of one chain past another. With little bond rotation and chain slippage, the energy of the fall cannot easily be converted into heat. To conserve the energy of the fall, the molecules move and then quickly return to their original position. At room temperature, consequently, the ball deforms on impact and then immediately returns to a spherical shape, cause the ball to bounce back to almost the same height as dropped. This phenomena is very temperature dependent. If cooled to about -40o C, these collisions become inelastic and the ball will not bounce well.

• The ball which does not bounce well is make from polynorbornene, which has a 5-membered ring as part of the chain structure. Although this group restricts the movement, the molecule absorbs most of the energy of a fall. With more degrees of molecular freedom, this polymer does not quickly return to its original shape. Thus, at room temperature, the energy of the fall is absorbed within the molecules in the form of heat. Even cooling this ball in the freezer changes its elastic properties so that a small bounce can be observed.

Your students may think it's magic, but we all know "It's Science!"

## Try This!

This has great information for teachers on implementing this activity into a course. It contains a full set of directions for a teacher as well as a full student guide to use. It was written by the President's Council of Student Advisors.

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## Try This!

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Source: Keith Zeise: Rufus King High School

Check out more explanations and extensions!

## What Else is There?

If you're interested in watching more of my demonstrations, checkout my playlist,