Think! Astronaughts are not weightless, they just appear that way?

Question

Because they are orbiting the earth at exactly the same rate as there spaceship. (orbiting means falling towards and moving away at the same rate). They appear to be weightless, but are not.

If the spaceship stopped they would fall to Earth pretty rapidly.

I thought I was going mad trying to explain this to people, they didn't get it, I'm just trying to work out if that's correct or not.

See: Collette H. 's answer, that's the sort of thing I'm up against here!

OK, I have now added a new question, as I realise what the question really is!

Answer 1

Actually at the very moment they are weightless. The thing is that even though they are weightless they still have their mass. They cannot feel any gravitational force pulling them, but they still have inertia.

The same way when you are falling down, you will feel weightless. The astronauts are all falling towards the earth, but at the same time they are moving with great speed to perpindicular direction. So they are "falling down" towards earth, but earth is moving away under them. So this means that they start to circle earth. Constantly "falling" thus feeling weightless.

Answer 2

Some of the previous answers have got parts right but not one is entirely correct, even the ones not intended to be nonsense!

Every object has mass irrespective of whether it's a solid object or a cloud of hydrogen gas in space.

The mass of a thing is its volume times its average density. This is irrespective of gravity.

A thing exerts a gravitational field, always an attractive force, directly proportional to its mass.

In a gravitational field a mass experiences 'weight', which is its mass times the gravitational field strength relative to the average gravity at the Earth's surface (mass X g). At the Earth's surface the gravity field, by definition, =1. Therefore at the Earth's surface mass is the same 'size' as weight.

The gravities of two (or more) objects are additive and create a pull towards each other.

Gravity obeys the inverse square Law, double the distance, quarter the gravitational pull; triple the distance one ninth the pull, etc. Since weight is a result of gravity this falls to 1/4, 1/9th etc.

At a certain distance the pull (i.e. gravity) becomes negligible and since weight = mass x g, weight becomes negligible, or weightless. At this point your astronauts do not appear weightless, they ARE weightless, but their mass is unchanged.

Speed has nothing to do with it, orbiting has nothing to do with it, only distance from a significant gravity field counts.

A moving object has momentum, mass X speed, therefore moving weightless bodies in space have the same momentum as if they were on Earth.

A still object has inertia, a resistance to movement, m X F, where F is the force required to overcome inertia.

Therefore any answer referring to the inertia of a moving object is nonsense and should be ignored.

A non-moving weightless body in space has the same inertia as on Earth.

I think that covers most of the simple bases.

Answer 3

The astronauts are orbiting the Earth all by themselves--they don't need the spaceship to do this (except initially to give 'em a push in the rear when going into orbit).

They are undergoing centripetal acceleration under the tug of the Earth's gravity.

When an astronaut (or any piece of space-stuff) blasts off from Earth, they face one of three fates:

1. Escape from the Earth's gravity, if they reach "escape velocity"--about 25,000 miles/hour.
2. Falling back to Earth. Wrong direction and/or too slow on takeoff.
3. Orbiting the Earth. They can go into orbit if they reach a desirable altitude at the right velocity.The lower the altitude, the HIGHER the velocity to stay in orbit.

For the international space station, at 220 miles up, the velocity has to be about 17,200 mph. It zips around the Earth about every 91 minutes.

Communication satellites, orbiting way up there at about 23,000 miles altitude, only have to travel at around 6,800 mph--just the right speed to orbit the Earth once every 24 hours. When they are launched, they are "aimed" to travel in the same direction as the rotation of the Earth, making them appear to "hang," stationary above the Earth.

Here's a cool calculator for figuring velocities, altitudes, and periods of orbit (you can fill in any blank and it will fill in the others):

http://hyperphysics.phy-astr.gsu.edu/hbase/orbv3.html

Answer 4

Heres a think that will amuse you more. Airplanes simple and generally have to go faster to go higher because of the way wings work.

But as far as orbital dynamics are concerned you have a faster speed at smaller orbital periods and the further out you go the slower you have to be.
But the real funny bit is to change the desired orbital height. There are parabolic curves and strange geometric verlocity changes that are the opposite of what one would expect.
Slow down so you are pulling away less, which means gravity has a net affect pulling you to earth and speeds you up. Then if you boost your verlocity out you can finaly get a further away orbit.

Answer 5

Remember they are past the field of gravity. Earth is the only planet with that field. The reason for this is that when God created the heavens and earth (Genesis 1:1) he planed it to be a place for man and beast to reside. If there wasn't gravity then we would all be wearing space suits on earth. But in "outer space" there is no gravity. Nor on any other planet. And when you say If the spaceship stopped they would fall to earth rapidly, well don't you think they stop while they are doing their research?

Answer 6

There is I think great deal of confusion. Let us go step by step. Astronaut's mass remains unchanged. What changes is his weight. This due to change in Acceleration due to Gravity. This on Earth at sea level is 32feet/sec^2 in FPS units or 9.80 Meters/sec^2 in SI units(call it g) As the altitude increases g reduces.In a geosynchronous elliptical orbit for earth this almost becomes negligible. Mass* acceration due to gravity gives us weight. Since g=zero weight becomes zero and this is the weightless state in space. Therefore Astronauts are Weightless in space. As long as he is in orbit he would continue to be weightless and as the space craft starts its descent he would start feeling his weight again gradually as the altitude above earth decreases. All other planets and satellites too have their own "g" for example on the Moon the gravity is 1/6 of what it is on earth. Same way on Jupiter "g"would be many times more than on Earth because of gigantic size of Jupiter. One question remains. On What does "g" depend? Primarily on the size of the planet. It comes about due to Newtons law of universal gravitation. As per this law any two bodies in this universe attract each other with a force which is directly proportional to the product of their masses and inversely proportional to the square of distance between them. Lastly if the space craft stopped what would happen?An orbitting craft has momentum which cannot be destroyed and hence if for some hypothetical reason force of gravity stops the craft would travel in a straight line as per Newtons first law. If the space ship stopped he would not fall to Earth but would continue in a straight line just as the space craft does.

Answer 7

Quite a good point and it makes perfect sense....and it's true. However, when the Apollo astronauts were headed towards the moon, they were weightless. At that point they were not orbiting anything. Hmmm...

There is no (Negligible) gravity away from planets so they truly are weightless.

Answer 8

Yes, robbed of the velocity that is trying to send the spaceship away from earth, there would be nothing to counteract earth's gravity.

Answer 9

I think that only goes for astronauts who are in actual orbit.

Anyway, they are weighless, as far as pressure on the surface that is accepted as pointing "down" goes - there is no pressure if they are at rest. On the other hand, they still have their mass (mass being equal to weight only in special circumstances, as in "on the sea-level, on Earth").

Answer 10

If there spaceship would stop they would all be thrown through the nearest wall in a straight line in front of them at about 17,000 MPH