How much does a body weight in free fall?

[patowlmc]

Homework Statement

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

Was that the correct answer?


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

 

[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?

 

[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?

 

[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

 

[rwisz]

I would like to clarify that the weight of an object is a measure of the force of gravity acting on it, and it is different from its mass. In free fall, an object is in a state of weightlessness, meaning that it is not experiencing a normal force from a surface and is only subject to the force of gravity. Therefore, in this situation, the object would not have a weight as there is no supporting surface to exert a normal force on it.

However, if we consider the weight in a non-inertial reference frame, such as the elevator in free fall, the apparent weight of the object would be zero since the elevator is also falling with the same acceleration as the object. This is known as the equivalence principle in physics.

In conclusion, the answer to the question would depend on the context and how the term "weight" is being used. In terms of the force of gravity, the object would have a weight of 490 N, but in terms of its apparent weight in the elevator, it would be zero. I hope this clarifies the concept for you.