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

1. Jun 1, 2009

### cragar

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 .

2. Jun 1, 2009

### CompuChip

Re: Weight?

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).

3. Jun 1, 2009

### cragar

Re: Weight?

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 .

4. Jun 1, 2009

### Staff: Mentor

Re: Weight?

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

5. Jun 1, 2009

### coverme

Re: Weight?

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 donot move
mg=R the weigth is measurement of R