why no gravity in orbit?

Question

if the moon that is +170,000 miles away is caught in earths gravity then why 100 mile up do astronauts not feel its effect?

Answer 1

there is gravity, but the astronauts are "falling" toward the earth at the same rate they are going around it, so they "fall" forever. If they stopped going around, they would fall back to earth. The moon is also falling around the earth, but considerable further away.

Answer 2

There is gravity in orbit. It's what keeps them in orbit. Otherwise they would fly off in a straight line at constant speed. However, gravity accelerates all objects at the same rate. So the spacecraft, the astronaut in the spacecraft, and everything else in the spacecraft is falling under the influence of gravity at the same rate, so you feel weightless. The same would be true of an astronaut in a box that was simply falling straight down to Earth.

As a side note, you never really "feel" the effect of gravity. Your subjective experience of "weight" is really the normal force of the floor pushing you up (acting only on your feet), not the gravity pulling you down (acting on all parts of your body equally). In orbit, there is no need for the walls of the shuttle to push the astronauts to keep them in orbit at the same rate as the shuttle, because under gravity all objects fall at the same rate, so no normal force.

As a second side note, it should not be that hard to understand how gravity keeps the shuttle in orbit rather than forcing everyone to the ground immediately. Tie a string to a ball and whirl it over your head. There is a lot of tension in the string when you do this, so that must mean that there is a pulling force on the ball that is directed, not forward or backwards, but directly to the center of the circle to keep it in orbit. Otherwise it would fly across the room. Exactly the same thing with the shuttle or the Moon in orbit, except with gravity instead of string tension providing the force.

Answer 3

Suppose you were in a falling elevator. You would be falling at the same rate as the elevator and would feel weightless even though gravity is working on both you and the elevator.

The same thing happens with spacecraft in orbit. The gravity keeps both you and the spacecraft in orbit. But since you are both falling at the same rate, you have the experience of weightlessness. In reality, there is a very, very slight difference between the gravitational force on one side of the spacecraft as on the other. This effect is why those inside the spacecraft experience 'micro-gravity'.

Answer 4

I can vaguely remember my old dad explaining this bad boy...

As I remember it, there is gravity, as a planet is bigger than an astronaut, as so the astronaut is subject to the gravity generated by the planet's mass. BUT - they are going around the planet, so they are, in effect, falling sideways. It's a bit mad-sounding, but it's the same effect that keeps the moon going around us, and us going around the sun. The reason the astronaut doesn't plummet to earth is because a) - they are so far away, and b) - because the earth is curved. So by the time they reach the patch of space where they should fall to earth, the curvature of the planet has moved and they need to fall further, by which time the curve has moved so they need to fall further and so on and so on.

Physics isn't my strong suit... :)

Answer 5

It's an equilibrium between gravity and centrifugal force. For each spaceship speed, there is a distance from the earth where it will be in equilibrium.

There is an interesting project which is to tie two space shuttle with a mile long wire. The first one would then be on an orbit slightly above what it should for the equilibrium, and the other, slightly under. The wire would then keep them in place because they would both pull on their side and result in an equilibrium. The reason for doing that is that it would create a weak, yet existing gravitation in both craft. That can be interesting if only to prevent dust to float constantly as in a spacecraft under 0-gravity.

Answer 6

Of course astronauts experience gravity.

The effect of the gravitational pull is to keep them in orbit. Without that force they would travel in a straight line. (Newton-one).

Answer 7

it is quite easy to understand by thinking a little bit. if u r below the orbit of earth, u are falling straight to earth. if away , then u r moving away. but at the orbit, the rotio of falling ane moving away is exactly the same, that's why the body remains in the orbit for ever

Answer 8

they do.
when they are so high up, they are attracted toward the moon rather than falling in the earth's gravity.

Answer 9

because I turn it off...

Answer 10

That's just one of the mysteries of the universe........