Question

a 40-kg crate is at rest on a level surface. If the coefficient of static friction between the crate and the surface is 0.69, what is the horizontal force is required to get the crate moving?

Answer 1

What is the equation for friction force? Another question, what happens if you push someone with the same force as they're pushing back at you? Do you move or stay still?

Answer 2

I know the answer, but I want you to understand why rather than just give it to you.

Answer 3

Ff = µFn
where:
µ = coefficient of friction (static or kinetic)
Fn = magnitude of normal force

Answer 4

stay still.

Answer 5

Alright, so what's normal force? You already know the coefficient of friction, so that's really all you need to find the friction force.

So now after you find that, you'll find the friction force. If you have another force equal to this pushing on the object, the object won't move correct? So you just need any force that's greater than what you're about to calculate for the friction force! This should make sense since you can move a large sofa if you push hard enough, or you could get a giant wrecking ball which will use a lot more force and move the sofa that way too. But a cat pushing on a sofa won't be strong enough to overcome this force.

Answer 6

so,
µ= 0.69
Fn= 40 x 9.8

then I will use this formula : Ff = µFn?

Am I right?

Answer 7

Yeah, I think so, you just gotta plug it in and you're done.

Answer 8

Thanks @Kainui :) You've helped a lot :)