# Homework help regarding forces of friction and their directions

#### MechRocket

The Problem

http://img15.imgspot.com/u/07/118/16/friction.JPG [Broken]

What I Think

http://img15.imgspot.com/u/07/118/16/think.JPG [Broken]

The Correct Solution

http://img15.imgspot.com/u/07/118/16/solution.JPG [Broken]

What Is Confusing Me

Shouldn't the force of friction on the slab be pointed to the left? I knew the force of friction on the block is pointed to the left (because friction will oppose movement), so I naturally assumed this force to the left also acts on the slab (the two surfaces are touching after all).

I just cannot see why the friction force on the slab is to the right.

Thanks a lot! :)

Last edited by a moderator:
Related Introductory Physics Homework Help News on Phys.org

Picture instead of the slab remaining stationary and the block sliding right, the block standing still and i the slab is sliding left. . . then which direction will oppose motion direction?

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving