1. Before starting:
there are 2 surfaces along which we may have normal and frictional forces
If there are no friction at all top box will stay in place while bottom moving to the left
If you are standing on bottom box, to you it will look like top box is moving to the right, that means friction acting on top is directed opposite
So frictional force acting on top box is opposite to its apparent motion
Using Newton’s 3rd law force acting on bottom box while it is rubbing against top is equal but opposite
If bottom box moves to the left then there will be a frictional force between box and table opposing the motion. T
NAB
Ffr AB wA
Fapp N
-FfrAB
-NAB
Ffr wB
Now about normal forces, again along 2 surfaces.
Normal force acting on top box coming from bottom box.
And according Newton’s 3rd law force acting on bottom box
Normal force acting on bottom box coming from the table
Now weight of the top box – it acts on the top box
Weight acting on bottom box
Force applied to bottom box
If top box is tied up, then you have to put tensional force on top box