# Homework Help: Inertial forces

1. Nov 16, 2007

### olga11

1. The problem statement, all variables and given/known data
If I act a force on a system consisting of a heavy and light body in
contact with each other from the side of the heavy body and then I act
the same force from the side of the light body, the inertial force
between the two bodies would be the same?

2. Relevant equations

3. The attempt at a solution

I know from experience that the inertial force is bigger in the first case
Does friction has to do with the proof?

2. Nov 16, 2007

### Dick

The contact force between the objects has to accelerate the body that you are not pushing on directly. So if you push on the lighter one, the contact force is greater than if you push on the heavier one. Nothing to do with friction.

3. Nov 17, 2007

### olga11

Let me see if I got it right.

If the masses m (the light one) and M (the heavy one) are a system of bodies, then no matter on which side I act the force F, the acceleration will be the same, i.e. a.
If I act the force F on the mass m, the contact force F΄ must accelerate the mass M to a.
If I act the force F on the mass M, the contact force F΄΄ must accelerate the mass m to a.
Since a is the same and M>m, then F΄>F΄΄

If there is friction, the only difference is that I will have another acceleration, i.e. a΄

Last edited: Nov 17, 2007
4. Nov 17, 2007

### Dick

Right, exactly. Where a=F/(m+M). I couldn't have put it better myself.

5. Nov 17, 2007

### olga11

You have been very helpful. I would dare to ask another question. I will put it here,too.

A bubble m(t) is in a spaceship with zero gravity.
It seems that the bubble's motion is due to a force F=k.m^2, where k is a constant.
Could this force be due to the acceleration of the spaceship?