What causes weightlessness in a free fall?

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Discussion Overview

The discussion revolves around the concept of weightlessness experienced during free fall, exploring its implications in both Newtonian physics and Einstein's theory of general relativity. Participants examine historical perspectives and definitions related to weight and the sensations associated with free fall.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants note that Einstein claimed a person in free fall feels no weight, questioning whether Newton had a similar realization.
  • Others argue that Newton did not recognize this concept, citing an anecdote of a person who fell and reported feeling 'weightless'.
  • It is suggested that the definitions of 'weight', 'weightless', and 'felt' are crucial to understanding the discussion.
  • One participant asserts that while one might feel weightless in free fall due to the cancellation of forces, this is not accurate in Newtonian physics, where gravity is the only acting force.
  • Another participant clarifies that in general relativity, free fall does not involve a force acting on the object, leading to the conclusion that one is indeed weightless in this framework.

Areas of Agreement / Disagreement

Participants express differing views on the nature of weightlessness in free fall, with some emphasizing the sensation of weightlessness and others focusing on the physical forces at play. The discussion remains unresolved regarding the interpretations of weight and the implications in different physical theories.

Contextual Notes

There are limitations in the definitions of 'weight' and 'weightless', as well as the interpretations of free fall in both Newtonian and relativistic contexts. The discussion highlights the complexity of these concepts without reaching a consensus.

chaszz
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Einstein said one his happiest realizations was that a person in free fall would feel no weight. Unless I am mistaken he said this. But didn't Newton realize this?
 
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I don't think Newton did realize this. Einstein was given a huge hint by a guy fell 60ft and lived to tell the tale. He is reported to have said he felt 'weightless' whilst falling.
 
It depends on the definition of 'weight', 'weightless', and 'felt'.
 
You wouldn't actually be weightless in a freefall, but you would feel like it because the forces are canceled out.

Einstein did realize that an observer accelerating due to a rocket or other force is analogous to an observer accelerating due to gravity: http://www.astronomynotes.com/relativity/s3.htm he used this to formulate general relativity from special relativity
 
Viracocha said:
You wouldn't actually be weightless in a freefall, but you would feel like it because the forces are canceled out.
What forces are canceled out? In Newtonian physics there is no cancelation of forces for an object in free fall. There is only one force acting on such an object, and that force is gravity.

There is no cancelation of forces in general relativity, either. There is no force acting on an object in free fall in general relativity. Gravitation is not a force in general relativity. There is no local experiment that can distinguish free fall conditions from force-free conditions far removed from any gravitational source. The two situations are identical as far as general relativity is concerned.

Bottom line: You actually are weightless in a free fall in general relativity.
 

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