Momentum of a free falling object

[nebbione]

Homework Statement

In a physics exam I have this question: "what is the momentum of the weight force of an object in a free fall relative to its center of mass?"

Homework Equations

Is my answer right ?

The Attempt at a Solution

My answer is: "If we try to calculate the momentum, the center of reduction coincides with the center of mass, and the line of action of the force passes through the center of reduction, so the momenut is canceled"

 

[CWatters]

what is the momentum of the weight force of an object in a free fall relative to its center of mass?

I assume that should read..

"what is the moment of the weight force of an object in a free fall relative to its center of mass?"

Isn't the moment of the weight force allways zero because it allways acts through the center of mass?

 

[nebbione]

Ok yes i know that is zero the answer but can you explain me in details why ? (try to re-read my attempt at answering the question)

 

[CWatters]

Your answer seems fine. I suppose you could add the maths. Something along these lines..

http://theory.uwinnipeg.ca/physics/rot/node4.html

 

[Nickie]

Your answer is partially correct. In a free fall, the weight force acts on the object's center of mass, making the center of mass the center of reduction. However, the momentum is not canceled, it is conserved. The momentum of the object in a free fall will remain constant as long as no external forces act on it. This is known as the principle of conservation of momentum. So the momentum of the weight force of an object in a free fall relative to its center of mass is equal to the momentum of the object itself, which is constant.