8. A spaceship is in orbit around the earth at an altitude of 12 000 miles. Whic

Question

8. A spaceship is in orbit around the earth at an altitude of 12 000 miles. Which one of the following statements best explains why the astronauts experience “weightlessness?”

   A.   The centripetal force of the earth on the astronaut in orbit is zero newtons.

   B.   The force of the earth on the spaceship and the force of the spaceship on the earth cancel because they are equal in magnitude but opposite in direction.

   C.   The spaceship is in free fall and its floor cannot press upwards on the astronauts.

   D.   The force of gravity decreases as the inverse square of the distance from the earth's center.(incorrect)

   E.   The pull of the earth on the spaceship is canceled by the pull of the other planets.

Explanation / Answer

Option C

So now lets think of weightlessness. When you are in a car on a hill or a theme park ride that made you feel weightless? I hope so or else this might not make sense.

As you go up a hill or a ride, you sink into your seat because you are being pushed up. This is why you "sink". Then at just the right moment, (at the top of a hill for example) the thing that is pushing you, like a seat, is moving at the same speed you are. This means it is no longer pushing you. When you are not being pushed you feel weightless. Then gravity kicks in and pulls you down back into your seat. Now that your butt is in the seat you no longer feel weightless because you are pushing on the seat.

So in space, the astronauts are basically falling at the same speed of their ship. This happens because the force of gravity is so small at the high of altitude, but it is still there. So they can "float" for a very long time. The closer they come to earth to more gravity attracts them and the faster they fall.

Just remember that when you are not touching anything you feel weightless, and when 2 things are moving at the speed, nothing is touching.

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