Pump It Up!

This is a great experiment for a teacher to do with a class.

What You'll Need:

Basketball (or other ball that can be inflated very hard)

A bicycle pump

A needle valve adapter for inflating balls (available at sporting goods stores)

A balance able to measure 1 gram or less (about a paper clip's mass)

Before you start, use the balance to measure small objects, like dimes and pennies. This will help you get used to what tiny measurements mean.

Steps:

1) Use the needle valve to let the air out of the ball. Slowly pump the ball back up until it is round, but still feels squishy.

2) Put the ball on the scale and write down how much it weighs.

3) Take the ball off the scale. Pump the ball up until it feels very stiff. (Don't pump too hard. You might pop the ball!)

4) Predict: Do you think the ball now weighs: a) more than before, b) less than before, c) the same. Write down your prediction.

5) Weigh the ball and write it down. Did the weight change?

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