# Forces on an object on a slope

• Sep 19th 2012, 02:27 AM
Stuck Man
Forces on an object on a slope
Are the answers correct? I feel that the friction force is wrong with number 3.
• Sep 19th 2012, 04:52 AM
chiro
Re: Forces on an object on a slope
Hey Stuck Man.

Just a question about the friction: is the friction a two way force (in other words, if you drag something both up and down the ramp does it oppose it both ways)?

If this is the case you might want to check out the friction vector for number 4 since it implies that friction actually helps the object go up the ramp.
• Sep 19th 2012, 05:15 AM
topsquark
Re: Forces on an object on a slope
Quote:

Originally Posted by Stuck Man
Are the answers correct? I feel that the friction force is wrong with number 3.

You are correct for both answers.

As far as friction is concerned, kinetic friction is easy: it's always opposing the motion of the object. Static friction is a little harder, but consider for diagram 3...The problem states that the object is going to be moving up the slope. So the friction force is down the slope.

So why is the friction going up the slope in problem 4?

-Dan
• Sep 19th 2012, 05:40 AM
Stuck Man
Re: Forces on an object on a slope
I can understand it now. Friction acts in a direction to oppose the motion of a body. The motion is up the slope with 3 and down with 4 and friction opposes the motion in each case.