00:01
Okay, so we've got some statements about frictional forces here, and we're just going to run through which ones are true, and we're going to base this off of the equations that we have that i have written out to the right -hand side here, and i'm just going to go through the kinetic friction statements first because i think that they're a little bit easier.
00:20
So from the equation that we have in the bottom, that tells us that the frictional force, the kinetic frictional force, is equal to the coefficient of kinetic friction.
00:30
That's that mu k times the normal force.
00:34
So that tells us that it is proportional to the normal force.
00:38
So that means that our first statement is going to be correct.
00:41
And that third statement is going to be incorrect.
00:44
Frictional forces should always be pointing opposite the direction of motion or opposite the direction of intended motion.
00:52
Just to kind of throw that in there.
00:54
And then when we're looking at the static frictional forces, so the three options we have is that the magnitude of the force of static friction may exceed the magnitude of the sum of all forces parallel to the plane, may be smaller than the magnitude of the sum of all forces in the plane, or can only be equal to.
01:14
So we do have that equation on the top that tells us that the frictional force, the static frictional force can be less than or equal to the coefficient of static friction times the normal force.
01:27
But what exactly does that mean? that means that if we have have an object and let's say we're applying some sort of force to it to get it to move.
01:40
And then if we're trying to get it to move, then we're going to have static friction working against us.
01:47
We could have basically so that static frictional force has an upper limit that if f push is greater than that maximum value, then we will have it start to move.
01:59
But if f push is less than that maximum value, then the frictional static force is going to just be equal to whatever that f pushes.
02:09
So let's see, let's write some cases down here.
02:12
So if f push is less than fs max, which would be when it's equal to the coefficient times the normal force, then we're going to have acceleration is equal to zero, which means the sum of our forces in the x in this case are going to be equal to zero...