Main Question or Discussion Point
why does astronaut feel ' no weight ' when in space?
A person in free-fall has all the bits of his body falling at the same rate. For this reason the astronaut does not sense that parts of his body want to move relative to other parts. But a person can be weightless in the Earth's atmosphere in free-fall too. This is how the train the astronauts. They have a special jet, which is often referred to as the vomit comet which is used soley for this purpose. The plane reaches a particular altitude and then dives at a rate of 9.8m/s2. The occupants are also falling at that rate to so if they are in the center of the jet at one time (off the floor etc) they never move from there unless there is a bit of drift. In fact this is how they filmed that movie Apollo 13.no idea said:why does astronaut feel ' no weight ' when in space?
Free fall is locally indistinguishable from a gravity free environment within some specified accuracy. However, free fall can be identified using the fact that the gravitational ``field lines'' are not perfectly parallel. Hence, free test particles will depart from inertial paths by detectable amounts over significant space-time displacements.broegger said:Is there NO way of determining whether you are actually in a gravity free enviroment or just experiencing a free fall (in both cases you fell no weight)?
Also (in the elevator car scenario) your feet are slightly closer to the Earth than your head, and so experience a fraction more gravitational force. The net result is a very slight force tending to stretch you lengthwise. These tidal forces would probably be too small to measure though, given the scale of the human body and the Earth.jdstokes said:Free fall is locally indistinguishable from a gravity free environment within some specified accuracy. However, free fall can be identified using the fact that the gravitational ``field lines'' are not perfectly parallel. Hence, free test particles will depart from inertial paths by detectable amounts over significant space-time displacements.
No, just against its inertia - but when the elevator gets to the bottom of the shaft, you will need to do some work to stop it...broegger said:What happens if you lift an object from the bottom to the top of this free-falling elevator; you are doing work against gravity? Is this non-sensable because is the whole elevator is accelerating at rate g?
As others have explained throughout this thread, the experience of "weightlessness" has nothing to do with the absence of gravity. You can experience weightlessness anytime you like right here on earth--albeit briefly--by just jumping into the air.mikej_45 said:you feel no "weight" in space because you can only find the weight of an object when gravity is present. Weight is not a constant figure...the higher you climb in altitude the less you will "weigh". So you feel no Weight" in space because weight does not exist without the forces of gravity acting upon the object in question.