Can the direction of friction force be opposite to the direction of motion?

In summary, to modify F=ma for static or kinetic friction, you will need to include a friction force vector in the free body diagram, with a magnitude of F=mu*N, where mu is the coefficient of friction and N is the normal force. However, for rolling objects, the direction of the friction force may differ from its traditional role of opposing motion.
  • #1
jrk613
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I was wondering how to modify F=ma and put in either static or kinetic friction coefficient. I assume it's something like F-(friction coef) but I'm just not sure, any ideas or websites someone can direct me to? thanks
 
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  • #2
jrk613 said:
I was wondering how to modify F=ma and put in either static or kinetic friction coefficient. I assume it's something like F-(friction coef) but I'm just not sure, any ideas or websites someone can direct me to? thanks

When you draw the free body diagram, you put in a friction force vector as one of the force vectors acting on the object. The direction of the friction force vector is to oppose motion of the object (whether static or kinetic friction), and the magnitude is generally F = mu * N, where mu is the coefficient of friction, and N is the normal force between the object and whatever it is rubbing on. N is often just the weight of the object, for example.
 
  • #3
berkeman said:
The direction of the friction force vector is to oppose motion of the object (whether static or kinetic friction)
Not the object as a whole. Only the motion of the contact point. For the FBD of a rolling wheel or an entire car for example, friction can turn out to be in the direction of motion.
 

1. What is the general formula for friction?

The general formula for friction is F = μN, where F is the force of friction, μ is the coefficient of friction, and N is the normal force.

2. How is the coefficient of friction determined?

The coefficient of friction is determined experimentally by measuring the force required to move an object across a surface divided by the normal force between the object and the surface.

3. What factors affect the coefficient of friction?

The coefficient of friction is affected by the nature of the two surfaces in contact, the roughness of the surfaces, and the presence of any lubricants or contaminants.

4. Can the coefficient of friction be greater than 1?

Yes, the coefficient of friction can be greater than 1. This means that the force of friction is greater than the normal force, resulting in a very strong resistance to motion.

5. How does friction affect the motion of an object?

Friction acts in the opposite direction of an object's motion, so it can slow down or stop the object's motion. It also helps to provide traction and stability for an object moving on a surface.

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