Weight
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Mass = the amount of material in an object. |
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Weight = mass x gravity = 100 Kg x 9.8 m/s/s
= 980 |
100
Kg
100
Kg
* Are all objects equally affected by gravity? (Yes!)
* Does a bullet that's been shot actually fall? (Yes!)
The folks at Newton
Your fuel gauge is below empty. Both engines of the cargo plane you're piloting have just sputtered and gone silent. The nose of the plane points down and you begin a terrifying dive toward Earth. In a panic, you make your way out of the cockpit and into the back of the plane where your parachute is stored. But a 2,000-kilogram crate is blocking your path. What do you do? |
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No problem! Since the weight of the crate on the plane's floor is actually zero, you would not have to lift it in opposition to gravity or slide it in opposition to its friction with the floor. The force required to overcome the inertia of the crate would be small enough to allow you to move it by pushing hard with your feet braced against a wall. How is this so? |
Let's look at the crate under
normal flight conditions. The weight of the crate pushes down against the
floor of the plane. What you might not realize is that the floor, which is
supported by the airplane's wings and the forces that keep the airplane
aloft, also pushes up against the crate. It pushes up with a force equal to
the weight of the crate, so inside the plane, you're aware of how heavy the
crate is.
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When your plane goes into free-fall, the crate is still pulled by gravity just as during a normal flight. But the floor is no longer pushing up on the crate, since it and the crate are now falling freely toward the earth. Gravity is still acting on both the crate and the plane, but inside the airplane, without the upward push from the floor, the crate now seems to be weightless. Both the crate and the pilot will float freely inside the airplane until something--like Earth--stops them. |
Astronauts in orbit experience weightlessness just
like objects in the falling aircraft. A space shuttle in orbit is actually in
a state of free-fall as it travels around Earth.
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Hard to
imagine? Picture yourself in a small spaceship a few meters above the ground.
Now face the setting sun and go in a straight line for about 100 kilometers (62
miles). If you go in a perfectly straight line, you should notice that Earth
is curving away from you.
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* Falling appears to be different for different objects. For instance, which
falls faster, a pen or a piece of paper? Why might one fall faster than the
other?
* In real life, when do you experience something like free-fall? For how long?
* Which falls faster, a one-ton plane or a ten-ton plane?
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VOCABULARY
acceleration change in speed during a certain
period of time
ascent going up
descent going down
force that which, when acting alone on
an object, causes a change in the motion of the object
gravity force on Earth which pulls all
objects toward its center
orbit falling around and around Earth
resistance a force opposing the motion of an object or opposing the forces
trying to set an object in motion
weightlessness feeling or being observed
as having no weight