# How much does a body weight in free fall?

1. Oct 9, 2011

### patowlmc

1. The problem statement, all variables and given/known data
Well, that's all, my mid-term exam came a question that asked me: if a body with mass of 50 kg was weighed on a scale that is inside an elevator in free fall, how much will it weight?

I supposed that the same it would weight on the surface, since gravity never stops acting on us, as long as we're on the earth, I.E. 490 N

P.D. Sorry for my TERRIBLE English, but I do what I Can to make my self as clear as possible :D

2. Oct 9, 2011

### WJSwanson

If the elevator is in free-fall, then that means the scale and the body are experiencing a net acceleration of equal magnitude. What might this tell you about the normal force of the scale acting on the body (which would be the same as the force of the body's acceleration acting on the scale)?

To illustrate, what do you perceive when you are riding in an elevator and it begins to accelerate downward?

3. Oct 9, 2011

### patowlmc

I think I get what you say.

So, since the elevator is in free fall, so are the objects, accelerating at the same speed, Which means they're bot moving downwards, so there's no Normal force acting on the scale.

Is that right?

4. Oct 9, 2011

### WJSwanson

That's correct. If the contents of the elevator are all accelerating at a rate of 9.8N/kg downward, there is no net force due to gravity between the objects. For some pretty interesting applications of this property, take a look at Wikipedia's page on "zero-gravity" plane rides:

http://en.wikipedia.org/wiki/Vomit_Comet