Friction and the Normal Force

In summary, the coefficient of friction is represented by F_f=\mu N and it is not necessary to distinguish between kinetic or static friction. When calculating frictional force, all forces contributing to the normal direction must be taken into account, including those from gravity and external pushes or pulls. Only one normal force exists for each surface and it is calculated using force analysis. This normal force is then used to calculate the frictional force using the equation Ffrict = Fnormal x coefficient of friction.
  • #1
amcavoy
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I know that [itex]F_f=\mu N[/itex] where mu is the coefficient of friction. I'm not concerned whether it's kinetic or static now, but I have a problem with the normal force. If I have two normal forces (for example, pushing a mop you have the normal from gravity and the normal from the angle at which the force is applied) how do I figure out the frictional force? Would I add the two normal vectors together? Or is the rule only to use the normal force from gravity?

Thanks,

Alex
 
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  • #2
apmcavoy said:
Would I add the two normal vectors together?

Yes, you would add them together. Whatever contributes to the force in the normal direction would need to be included. If the mop were on the space station, there'd still be friction if you were pushing on it, although you'd need to be braced against something to do it.:wink:
 
  • #3
In fact, there is only ONE normal force to any surface. The surface doesn't care whether the reaction is due to gravity or you pushing on it. All the surface "knows" is that if you push something onto it, it will push back equally as hard (Newton's first law), given the surface doesn't break :P

The method then would be to use force analysis again. With Fgrav going down, Fpush going down, and Fnormal going up. The equation looks something like Fgrav + Fpush - Fnormal = 0. If there are any other forces, add them in. Fnormal will change accordingly, and Fnormal is the force you are looking for in Ffrict = Fnormal x coefficient of friction. ^^

An example of you pulling instead of pushing: Fgrav - Fpull - Fnormal = 0.
 

1. What is friction?

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

2. How is friction related to the normal force?

The normal force is the force exerted by a surface on an object in contact with it. Friction is directly proportional to the normal force, meaning that as the normal force increases, so does friction.

3. What are the different types of friction?

There are four main types of friction: static friction, sliding friction, rolling friction, and fluid friction. Static friction occurs when there is no movement between two surfaces, while sliding friction occurs when two surfaces are sliding against each other. Rolling friction is the resistance to motion between a rolling object and a surface, and fluid friction occurs when an object moves through a fluid (such as air or water).

4. How does friction affect motion?

Friction acts as a resistance force, meaning that it can slow down or stop the motion of an object. It also converts kinetic energy (the energy of motion) into heat energy, which can cause objects to heat up.

5. How can friction be reduced or increased?

Friction can be reduced by using lubricants, such as oil or grease, to create a slippery layer between two surfaces. It can also be reduced by using smoother or more polished surfaces. Friction can be increased by applying more force between two surfaces or by making the surfaces rougher.

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