HOW FAST DOES IT FALL?

You Will Need:

• A long piece of wood, or cardboard (6 to 8 feet long is the best).

• Cardboard strips

• Masking tape

• 2 balls of different weights (a ping-pong ball, and a large marble make a good combination)

• A pile of books

• 2 pieces of the same kind of paper 

ABOUT FALLING OBJECTS

Once upon a time, everyone knew that objects fell at differnt speeds.  The bigger, or heavier the object, the faster it would fall.  Of course, nobody bothered to test this out, because, after all, they all knew it was true.  Everybody was happy with what they knew, and nobody bothered to ask how they knew it.

Then one day along came a man named Newton.  He was a curious sort of fellow, always wondering how things worked.  Newton wasn't satisfied with what everyone said, he had to check it out for himslef.  One of the things that Newton wanted to check out was how fast things fell.  He wasn't satisfied with what "everyone knew," he wanted to see it for himself.

Newton tried dropping differnt things to see how fast they fell.  Unfortunately, he found that the human eye can't see things quick enough to tell if they were hitting the ground at the same time.  To make it easier, he decided that he needed to slow down how fast his objects were falling.

Since he couldn't control the gravity, Newton decided that he needed to use something that would make the balls fall at an angle, instead of straight down.  That way, the weights would go toward the ground at the same speed, but they would move a greater distance.  What he did, was use an incline plane (a ramp) to make two different round weights (balls) roll slowly toward the ground.

Newton reasoned that the incline plane would be the same as falling, but done over a greater distance.  He said that if he took his incline plane and put it straight up and down, that would be the same as falling.  By increasing the angle, the balls would still be falling, but doing it over a greater distance. 

TESTING THE FALL

Let's see if we can duplicate Newton's experiments, and test how fast things fall.

1. Use the cardboard strips and masking tape to make sides on       your incline plane.
   

2. Take your two weights (balls) and hold them in your hands the same distance from the ground.  Drop both weights at the same time, and see which one hits the ground first.  Repeat several times, to make sure you get the same results.
   

3. Set one end of the the incline plane on a stack of books so that the top end is 10 to 12 inches off the floor, and the bottom end is on the floor.  The bottom end should be facing a wall, and about a foot away from it.
   

4. Starting with both weights (balls) at the top of the incline plane, release them both at the same time.  See which one reaches the bottom first.  Repeat several times, to make sure you get the same results.
   

5. Take one of the pieces of paper, and crumple it into a ball.  Holding the crumpled piece of paper in once hand, and the flat piece in the other hand, drop them both at the same time.  See which one hits the ground first.  Repeat several times, to make sure you get the same results.
   

EXPLAINING HOW IT WORKS

When you dropped the balls, you probably had a hard time telling which one hit the ground first, just like Newton did.  However, once you used the incline plane, it should have been easy to tell how fast the balls were falling.  Your two weights should have fallen at the same speed.  Or, in other words, they should have both reached the wall at the same time. 

Newton calculated that all objects fall at the same rate.  Not only that, but they accelerate (move faster and faster) as they are falling.  He further proved that the rate objects fall at is 32 feet per second per second on earth.  That means that in the fist second, the objects fall 32 feet.  In the second second, they 32 feet times 2 seconds, or 64 feet.  In the third second, they fall 32 feet times 3 seconds, or 96 feet, etc.

If that's true, then why didn't both of your pieces of paper fall at the same rate?

Although all objects fall at a rate of 32 feet per second per second, they all have what is know as a terminal velocity.  As the object is falling, the air friction pushes against it, and tries to slow it down.  As it speeds up, the air friction gets greater and greater, until it reaches a point where the object cannot accelerate any more.  This is called the objects "terminal velocity."

The terminal velocity of the flat piece of paper is much greater than the crumpled up piece.  That's because the terminal velocity is dependent upon how big an object is, how much surface area there is.  When you crumpled the piece of paper, you reduced the total surface area, causing less air friction, and a much higher terminal velocity.

This is how a parachute works.  When a person jumps out of an airplane, he falls at a rate of 32 feet per second per second.  However, the parachute has a much bigger surface area, so their terminal velocity changes, to a rate of about seven miles per hour.  This makes for an impact that is much easier to survive than would exist with a terminal velocity of about 190 miles per hour, which is what a person without a parachute will fall at.

Newton went on to do other experiments with falling objects.  He had a glass blower make him a glass tube that sealed on both ends.  Inside the tube, he put a steel ball, and a feather.  Then he sealed the tube, and removed all the air.

If you were to try dropping a steel ball, and a feather at the same time, the steel ball would hit the ground much sooner.  That's not because of the difference in weight, but because of the difference in surface area.  The feather has a greater surface area, thus a much lower terminal velocity.  However, when Newton did this experiment in his sealed glass tube, they both fell at the same rate.  That's because there was no air in the tube to slow down the fall of the feather.