Understanding Forces on a Box: Basic Physics Question"

[MattsVai]

Hi everyone! This is my first post so I thought it appropriate to start with a basic question and not give u guys a hard time :) ehehe

So imagine u have 1 box resting on a larger box. A force is applied to this larger box and the smaller box moves with the larger box without slipage.

My question is, if I were to draw up the FBD, what forces are being applied on the small box apart from Fn and Fg?

Cheers

 

[matthew baird]

Well isn't that it?? Apart from a rediculously small amount of drag, which force do you suppose is keeping the small box from sliding off the larger one? that's your hint..

 

[MattsVai]

Well, I am thinking apart from Fn + Fg there is a friction force keeping that small box stationary on top of the larger box. If that is the case there must be a balancing force because technically the small box is relatively stationary. So this means that we also have the applied force Fa on the small box too?

This results in 4 forces: Fn, Fg, Fa, Ff

Am I on the right track?

 

[matthew baird]

You are right to think that there is an equal/opposite of the static friction on the small box, but that force acts on the big box.
So, a revised list would be:
Fn,Fg,Fs where Fs=force of static friction

 

[MattsVai]

Makes sense... thanks a bunch :)