Weight=mg and if g is the acceleration due to gravity

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Discussion Overview

The discussion revolves around the concept of weight as defined by the equation weight = mg, where g represents the acceleration due to gravity. Participants explore the implications of this relationship, particularly in the context of standing still on the ground and the forces at play, including the normal force and the perception of weight during free-fall.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how they can be accelerating if they are not moving and their velocity is constant, seeking clarification on the application of force on Earth.
  • Another participant explains that while standing still, the normal force from the ground counteracts the gravitational force, resulting in no net acceleration.
  • A participant raises the point about feeling a force and references Einstein's assertion that one does not feel their weight while in free-fall.
  • Another participant counters that the concept of not feeling weight in free-fall is not exclusive to Einstein, as it has been understood since Newton's time.
  • A later reply reiterates the relationship between gravitational force and normal force, stating that the weight is a measurement of the normal force acting on the body.

Areas of Agreement / Disagreement

Participants express varying degrees of understanding regarding the concepts of weight, force, and acceleration. There is no consensus on the implications of these concepts, particularly concerning the experience of weight in different scenarios.

Contextual Notes

Some assumptions about the definitions of weight and force may not be explicitly stated, and the discussion relies on interpretations of Newton's laws and Einstein's theories without resolving potential ambiguities.

cragar
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this is probably a really dumb question but I just have to ask it when I am standing
on the ground my weight=mg and if g is the acceleration due to gravity .
but how am I accelerating I am not moving and my velocity is not changing , and how am I applying a force on Earth .
 
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Ordinarily you are not accelerating, because the floor is pushing back at you with precisely the same force. This is called the normal force. When there is no such thing as a floor (for example, you are jumping from an airplane or your elevator cables break) then the acceleration of the Earth produces the only force acting on you (except for things like friction) and you will accelerate (when jumping from an airplane, that's the whole point; when inside an elevator whose cables just broke it's a less pleasant effect).
 


ok I see , when we feel a force on our body if we feel , I guess what i am asking is will we always feel a force . didn't Einstein say that when we are in free-fall we can't feel our own weight .
 


You don't need Einstein for that, it worked this way since Newton.
 


cragar said:
this is probably a really dumb question but I just have to ask it when I am standing
on the ground my weight=mg and if g is the acceleration due to gravity .
but how am I accelerating I am not moving and my velocity is not changing , and how am I applying a force on Earth .

the Earth is trying to accelerate you towards the Earth but at same time surface of Earth obstructs ,by Newtons third law,the surface gives tou a force (R)
such that
mg-R=0, so you don't move
mg=R the weigth is measurement of R
 

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