I can not assume the sense of the friction force?

In summary, when solving statics problems, assuming the direction of the friction force using the equation F=uN may lead to incorrect results because the direction of friction is dependent on other variables and cannot be determined solely by the equation. Additionally, the equation F=uN is not a vector equation and cannot be used to determine direction.
  • #1
hyper
49
0
With all the mechanical forces in statics problems I can assume the sense and I might get a negative answer which implies I made the wrong assumption. But why can I not do this with the friction force when using the equation F=uN?
 
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  • #2
Because the direction of friction is not independent of other variables. For example, if you assume something slides to the right, then friction on it must point left.

Perhaps discussing a specific example would help, if you have one.
 
  • #3
Besides, the equation you mention is not a vector equation, so you can't use it to find direction. It can't be a vector equation, because in ordinary cases the normal force and frictional force are perpendicular.
 

1. What is the friction force?

The friction force is a force that opposes the motion of an object when it comes into contact with another surface.

2. How is friction force measured?

Friction force can be measured using a spring scale or a force sensor. The force required to overcome the friction and move the object is the measure of the friction force.

3. What factors affect the magnitude of friction force?

The magnitude of friction force is affected by factors such as the roughness of the surfaces in contact, the weight of the object, and the type of surface (e.g. smooth, rough, or lubricated).

4. Can the direction of friction force change?

Yes, the direction of friction force can change depending on the direction of motion of the object. For example, if the object is sliding to the left, the friction force will act to the right, and if it is sliding to the right, the friction force will act to the left.

5. How does friction force affect an object's motion?

Friction force acts in the opposite direction of an object's motion, so it can slow down or stop the object's motion. It can also cause an object to move in a curved or circular path. Without friction, objects would continue to move at a constant speed indefinitely.

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