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## Falling Bodies

What's a falling body? Drop a ball on the ground, the ball is now a falling body. Not that hard to understand right? Well, one thing you might not notice is that when the ball falls, it accelerates. One major thing that gives that away is that when it's in your hand, it doesn't move, right? So its velocity is zero, but since it begins to move, then the velocity is not zero anymore. So it accelerates!

And it keeps accelerating. Aristotle, one of the first "scientists," thought that a falling body immediately gained a velocity and then remained at this constant velocity until it was stopped. He also believed that a heavier body fell faster than a light object. Do you think that makes sense? A sheet of paper falls slower than a ball, right?

Another scientist named Galileo tried to imagine what would happen if it was an ideal situation. He thought that air pushed up against the sheet of paper, which explained why it fell slower. He thought air acted as friction--air friction. So he crumpled up the paper and dropped it, it fell a lot faster than before. But since the paper's weight did not change, the crumpled paper was not any heavier than before. Therefore, he proved Aristotle wrong. He believed that everything on Earth accelerated towards Earth at a constant acceleration if there was no air (in a vaccuum). An elephant would fall just as fast as a sheet of paper if there was no air. He was right.

At a given location on the earth and in the absence of air resistance, all objects fall with the same uniform acceleration. This acceleration is called the acceleration due to gravity and it is refered to commonly as g.
g = 9.8 m/s2 (metric)
g = 32 ft/s2 (English)

Get used to the metric system because from here on in, that is all that is going to be used because using the English system is just plain annoying, and no one uses it in science anyhow.

### Orbits and Free Fall

What exactly are orbits? From what you know, when something "enters" orbit it circles around the Earth, right?

This is what actually happens when something goes into orbit: Imagine what happens if you are standing on the tallest mountain in the world and you pick up your trusty ball and throw it as hard as you can. Well, you now know it will accelerate towards the ground until it hits the Earth. Since the Earth is round, if you throw it fast enough, it will never touch the ground. As the ball falls towards the ground, it falls with the bend of the Earth so that it will eventually hit you in the back of the head after coming completely around the Earth! (By the way, don't actually try to throw a ball around the Earth. You would need to throw it at about 7900 m/s on the surface of the Earth.)

That is actually what happens when you "enter" orbit. When you see a spaceship go into orbit, it is actually constantly falling towards the Earth except it keeps, well, missing it. Now if the spaceship is always falling then that means the things in the spaceship must be falling. They don't have weight but the still have the same mass (this is the difference between mass and weight--mass is how much "stuff" there is in an object, while weight is how much force is created because of gravity).

The person or object falling feels as if they have no weight at all since they are continually falling in the orbit. If you were in an elevator that suddenly began to free fall (Heaven forbid), you would feel weightless as well since you are falling with the elevator. This basically explains the feelings of weightlessness of astronaunts when they are in orbit. They are weightless, but they are not weightless because there is no gravity. They are weightless because they are falling with the spaceship.

Check out the Orbit Explorer in our games and fun stuff section to see how a body orbits another body.

Created by TQ Team 16600: Clyde Law, Chetan Taralekar, Jim Wang
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Team Coaches: Melanie Krieger, Chhaya Taralekar