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# Science Fair Projects: Physics by Tom Robinson

## GRAVITY

In the early days of science, it was generally accepted that heavier objects fell faster than light objects. In fact, Aristotle, a famous scientist during the fourth century B.C., tried to come up with a mathematical relationship between the weight of the object and how fast it fell. Nearly 2,000 years later, Galileo didn't think that was right. He tested several objects, without the technology we now have, and decided that it was the air that made certain objects fall more slowly than others, not their weight. What do you think?

## QUESTION

Why do some objects fall faster than others?

## EXPERIMENT OVERVIEW

In this experiment you'll be testing several objects to see what features determine how fast they fall. You'll be picking heavy and light objects, large and small objects, solid and hollow objects, and you'll drop them all. You will then be able to scientifically determine what makes one object fall faster than another.

## SCIENCE CONCEPT

Long ago, people generally believed that the heavier something was, the faster it would fall through the air. The person most famous for holding this belief was named Aristotle. Today, we have plenty of examples that back that claim up. For example, if you were in a helicopter and you dropped a Ping-Pong ball and a bowling ball out of the door at the same time, the bowling ball would hit the ground first. But since Ping-Pong balls and bowling balls aren't the same size, try another example. Drop a Ping-Pong ball and a golf ball and the Ping-Pong ball still loses. So what's the big deal?

In the 1500s, a man named Galileo tried to show that it really didn't matter how much an object weighed — that it would usually fall at the same speed as any other object, as long as you didn't have to take air into account. You've already looked at a few experiments about air and there are more to come, but for now, think about the effect air has on a falling object.

When you run down the street or open the window in your car, you feel the wind. If it's strong enough, it can make it hard to walk or run. Now imagine that you are falling through the air. The faster you go, the windier it feels and the harder it becomes to move. A heavier person wouldn't be affected as much as a light person would be. That is the idea of air resistance, and you'll explore it in this experiment.

## MATERIALS

1 object you would call “light” — e.g., feather

1 object you would call “heavy” — e.g., rock

1 object you would call “small” — e.g., plastic figurine

1 object you would call “large” — e.g., basketball

1 object you would call “solid” — e.g., croquet ball

1 object you would call “hollow” — e.g., Wiffle ball

4 other objects of your choice

1 sheet of paper

1 writing utensil

A platform or raised place from which you can drop these items. (The higher you can climb the better, but you must be sure that the area below is open and free of people. Dropping objects can be very dangerous.)

A partner who can tell you which object lands first

## PROCEDURE

You will be recording results from each test. An example is shown below:

Test: Light (object name, e.g., feather) vs. Heavy (object name, e.g., rock)

Light object (feather) — small, white, weighs almost nothing, about 3 inches long, not solid

Heavy object (rock) — medium sized, brown and black, weighs about the same as a baseball, about 3 inches in diameter, round, solid

Winner: The rock

• In order, test the following pairs and record your results:

Light — heavy

Small — large

Solid — hollow

Other pairings from your collection of objects

• When you have finished testing, look at the results and determine the factors that made objects fall the fastest.

## QUESTIONS FOR THE SCIENTIST

• Of your entire collection, which object fell the fastest?

• Which characteristics of this object made it fall fast?

• Which characteristics had no effect on how fast it fell?

• Which object fell the slowest?

• Which pairing showed the most significant differences in how fast the objects fell?

• What could you do to eliminate air from this experiment so you could test Galileo's claim?

## CONCLUSION

The shape of the object is a very important factor in how fast it falls. It's true that weight matters too — really light objects fall slowly no matter how they are shaped because once they start hitting the air, they immediately slow down. But the heavier the object, the more its shape matters. A simple test to verify this result is to drop a single sheet of notebook paper at the same time you drop a crumpled up piece of the same paper. Try it and you'll see the difference shape makes.

Modern science has shown us that if we take away air, objects will fall at the same speed no matter how big or small they are and no matter what shape they are. When the astronauts went to the moon, they dropped a feather and a hammer to see which would fall faster. On the moon, there is no air. (Astronauts wear special suits to help them breathe.) Can you guess what happened? The feather and hammer landed at the same time.

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#### THE EVERYTHING KIDS' SCIENCE EXPERIMENTS BOOK

By Tom Robinson

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