Which force is called weight?


by xCross
Tags: called, force, weight
Doc Al
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Jan7-11, 04:25 AM
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Quote Quote by Gallin View Post
So when is the normal force different than the gravitational one?
Whenever you are accelerating. For example, jump off of a bench and the normal force goes to zero yet the gravitational force hasn't changed. Or simply stand in an elevator while it accelerates upward--the normal force is now greater than the gravitational force.
Doc Al
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Jan7-11, 04:32 AM
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Quote Quote by Saw View Post
Each one has its own pair of 3rd Law forces. The 3rd Law pairs (acting on different objects) do not counteract each other.

Hence it is the mixture between two forces of different kind and opposite sign (which are not 3rd Law pairs and do act on the same object) what causes the equilibrium, isn’t it?
Exactly. 3rd law pairs can never produce equilibrium on their own, since they act on different bodies.

To me, physics should not use the word “reaction” in the context of 3rd Law. The two sides of a 3rd Law are really the two sides of the same thing. It is an interaction, a single phenomenon, having effects on both sides… What would you advise?
The 'action/reaction' terminology is old-fashioned and misleading, for exactly the reasons you point out. Avoid it! Much better to refer to them as 3rd law pairs.
Saw
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Jan7-11, 04:35 PM
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The 'action/reaction' terminology is old-fashioned and misleading, for exactly the reasons you point out. Avoid it! Much better to refer to them as 3rd law pairs.
Thanks a lot. I corrected my notes accordingly and now everything fits better in my head.
ashishsinghal
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Jan11-11, 08:47 AM
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Freely falling body is not weightless. It just doesnt feel any weight because one feels weight cause of the normal force acting on it
D H
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Jan11-11, 11:11 AM
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Quote Quote by ashishsinghal View Post
Freely falling body is not weightless. It just doesnt feel any weight because one feels weight cause of the normal force acting on it
That depends on what you mean by "weight". "Weight" is one of those semi-scientific terms that has multiple meanings. With one of those meanings, also called scale weight or apparent weight, a freely-falling body is weightless.


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