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Gravity

You Need
1 large ball of modeling clay
1 small ball of modeling clay
1 piece of writing paper
1 roll of string
1 clean garbage bag
1 roll of masking tape

What to Do
1. Hold a large ball of modeling clay in one hand, and a small ball of modeling clay in the other hand. Raise them as high as you can above your head, and have a partner tell you when the bottoms of both balls are level with one another. (See Figure 1.)

2. Predict what will happen when you drop the two modeling clay balls. Will the light one hit the floor first? Will the heavy one hit the floor first? Will they hit the
floor at the same time?3. Listen as the balls are dropped. Which ball hits the floor first?

4. Change the modeling clay balls so that the small one is even lighter and the big one is even heavier. Try the experiment again.

5. Find a safe place to test the dropping rates of the two balls from a greater height. Does it make a difference to the result?

6. Predict what will happen if you drop a modeling clay ball and a wad of paper at the same time. Test your prediction by doing the experiment!

7. How can you make the paper fall at the same rate as the modeling clay ball? Do it!

Many centuries ago, the Greek philosopher Aristotle argued that a heavy object would fall faster than a light one, and for centuries, people believed him. Then Galileo (according to legend) said, “Let's try it!” Aristotle was proven wrong. In the
absence of air resistance, a feather will fall as fast as a bowling ball! (To show this, you would have to do the experiment in a vacuum.) Both fall together, increasing their speed at a rate of about 9.8 metres per second, each second. (We say the acceleration is 9.8 metres per second per second, or 9.8 m/s2. On the moon, objects fall with an acceleration of just 1.6 m/s2, so if you did fall off a cliff on the moon, it would seem like slow motion!

A piece of paper will fall more slowly than a ball, because air resistance affects it more. (The force due to air esistance opposes the force of gravity.) Even when it is crumpled up, the paper will lose a race to a ball. Air resistance can be put to good use when you wish to slow your rate of fall from an airplane. A parachute is designed to maximize air esistance so that your rate of fall is manageable and relatively danger-free.

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