How can i be weightless n spacecraft that is still under a planets gravitional pull?

Answer 1

By falling all the time. Weightlessness is sometimes called free fall because that is what an orbit is. It is falling toward the Earth whose surface is curved and you are going sideways so fast that it curves out from under you as fast as you fall toward it. So you are falling around the Earth when in orbit. It is exactly like the free fall rides in amusement parks, only those rides have no 17,500 MPH sideways motion to allow the fall to go on forever.

Answer 2

You are weightless in an orbiting spacecraft because you and the spacecraft are all travelling at the same speed.

If you throw an object it will follow a parabolic curve until it hits the ground. If you could throw an object far enough, the Earth's surface will be curving away beneath the object at the same rate as the object is curving downwards due to gravity. That is known as an orbit. In a sense a spacecraft in orbit is constantly falling but can never meet the ground.

Since everything is falling at the same rate, inside the spacecraft everything appears to be weightless. There is no force pushing you against the floor because you and the floor are both moving in the same direction at the same speed. You can't register a weight on a scale for the same reason.

If you're having trouble imagining this, consider yourself on a train. If you are standing up on a train while it is stationary you don't feel any forward or backward movement. If you stand up while the train is travelling at a constant speed you don't feel the movement either because you are travelling at the same speed as the train. You are not thrown against the back of the train even though it is going at up to 100mph because you are also going at 100mph. You feel the force as the train slows down or speeds up, but once it is going at a steady speed you feel the same as if you were standing on a motionless train, and you can walk in any direction as easily as if you were on a motionless train.

Now imagine that in all three dimensions, not just forward and backwards, and you have the situation in an orbiting spacecraft. Everything is falling around the Earth in the same direction at the same speed, so nothing sits on the floor, nothing falls toward the floor, and nothing exerts a force on a scale. You can move fowards, backwards, sideways, up or down with equal ease, hence you are termed weightless.

Answer 3

An orbit really is not the same as a freefall.

I will explain orbits and ignore freefall. Consider a circular orbit around the Earth (like the space shuttle). Gravity is still pulling on the shuttle with a force of: Fg = k*m/r^2. Where k is a constant, m is the shuttle mass and r is the distance from the center of the Earth. Since the orbit is in a circle, centripital acceleration works on the shuttle creating centrifugal force. This force is Fc = m*v^2/r.

If you set the two forces equal, you can determine how fast the shuttle must travel at any altitude to be in orbit.

When you are in orbit, gravity is pulling you down and centrifugal force is throwing you out, The definition of an orbit is that these two forces cancel out.

So, in answer to your question, you and the spacecraft both have the force of gravity but you both have centrifugal force as well. The two balance out so that you and your spacecraft are weightless.

Answer 4

BEcause you are only weightless relative to the spacecraft, since orbit is technically a very long controlled fall. That's why you become weightless in a plane that is diving. Orbit is the same, but for hours, days or months at a time.

Answer 5

First, Phil2 – ok, you are correct about lifting the arm, that is related to mass and not weight, so that was cheating. Experience is still valid as a rock wouldn’t ask the question, but more importantly the question really relates to frames of reference – ie. why is the inside of a spacecraft an inertial frame of reference ?
Bottom line is this question can be answered definitively using classical physics (Newton and Galileo), Einstein is only required if you wish to take the question to further depths on the nature of gravity.
So, I assure you, the following IS the answer, in terms of a tennis ball (a kind of soft rock).

On a train
1) Roll a tennis ball off the table and it follows a curved path to the floor. We attribute this result to the weight of the ball, under the influence of gravity

On a spacecraft in orbit
1) A spacecraft in orbit is in free fall (see other responses below, eg. my first one, JasonT)
2) All objects fall at the same rate under the influence of gravity (Galileo), so in free fall everything in the spacecraft is falling at the same rate; you, the tennis ball, the table, the floor
3) Roll the ball off the table and it will follow a straight line parallel to the plane of the table top, in constant motion (Isaac Newton – first law of motion) – It doesn’t fall to the floor, so it must be weightless ???
4) In truth when the ball rolls off the table it does fall, just as the ball did on the train. However in the spacecraft, everything else is also falling at the same rate. As the table, floor and ball are all falling at the same rate, the ball appears to follow a straight line, and doesn’t move to the floor. This is all about perspective (or experience), as described in bullets 5 and 6 below.
5) Observer in the spacecraft – The ball rolls off the table and continues in a straight line. We are all weightless, and existing in an inertial frame of reference
6) Observer on the ground (with a big telescope, looking inside the spacecraft) – The ball rolls off the table and falls, following exactly the same curved trajectory as that which rolled off the table on the train. However, as described in bullet 4, the whole spacecraft is also falling so the ball never reaches the floor and continues on a path parallel to the plane of the table top

Hope this is a clear explanation. You are not weightless in the spacecraft, however the laws governing your motion inside, and with reference to, the spacecraft are not influenced by your weight, but purely by Newton’s Laws of Motion;
"An object at rest will remain at rest unless acted upon by an external and unbalanced force. An object in motion will remain in motion unless acted upon by an external and unbalanced force" - Newton
See
1) http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion
2) http://en.wikipedia.org/wiki/Inertial_frame

Pretzels – you will be interested to note that the second reference describes the fictitious nature of your centrifugal force. That is why your answer is incorrect

Answer 6

I still think the best answer is the one I gave you under the "Physics" heading...

"You can think of it in 2 ways:

1. You are in free fall with the speed of your fall matching the curvature of the Earth as you travel forwards in your orbit. (Actually, this can be a constant speed giving a circular orbit, or varying to give an elliptical orbit)

2. Your rotational speed and radius of orbit are such as to just match your weight, so that you're in equilibrium and "weightless". i.e. m.v^2/r (or m.r.w^2) = m.g where m is your mass, r radius, v velocity, w (I can't write omega) rotational velocity in rad/sec. and g acceleration due to gravity.

There is a 3rd way that Einstein could explain to you whereby you're following the shortest path in the space-time continuum!"

How many times have you asked this question?


PS Eddiemc2, it's nothing to do with "experiencing" weight or not; a senseless rock doesn't experience anything. It has weight in the prescence of gravity, or under an acceleration (which is indistinguishable from gravity) - zero gravity, then zero weight.

And you don't have to overcome the weight of your arm when lifting it in zero G. All you have to do is overcome it's inertia - i.e. apply a force to accelerate its MASS (not weight).
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ADDENDUM
Eddie, I think you are correct under Newtonian physics. Rather than being weightless, your weight and centrigual force (let's call it that for convenience) are in equilibrium. Hence, my quotation marks around the word, originally.

However, it was Einstein who equated gravity and acceleration, so nowadays it is correct to use the term "weightless".

Answer 7

If the planes speed ( down ) is same to gravitional pull you be weightless.

Answer 8

You are mistaking 'weight' for 'mass'. The earth's gravity acts on your mass but you only feel the effect called weight when either you come into contact with the source of gravity or you accelerate or decelerate.

Answer 9

I can't be sure, but I believe it's a combination of inertia and near 0 gravity that makes us weightless.

For instance, if the craft didn't move you might weigh, say 3 pounds? But since it IS moving, it create a force that pushes OUTWARD as well, therefore equalizing the effects

Answer 10

easy when you travel faster than the power gravitation. then u Will be floating in the air.