Static friction confusion -- Friction versus the Normal force

[nemo11]

I am a bit confused.
We have an inclined plane.
So I know that Ffmax=μ*N and μ is the coefficient of friction calculated as tgθ (θ is the angle at which the body is on the verge of sliding) and also Ff<=Ffmax
And we know that the force that makes the body slide is mgsinθ.
So as the angle increases this force(mgsinθ) increases but N=mgcosθ decreases . So my question is how does the friction force increases if N decreases ?

 

[KushalBhanot]

It does not .

 

[scottdave]

I'm not sure what you mean by "frictional force increases". Unless you mean that the amount of friction will always be "just enough" to keep it from sliding, up until the point that the force is greater than the maximum available frictional force (Ffmax). Think about this. On a level surface, Ffmax is the greatest, but if there are no external forces trying to slide, then the friction force is zero.

 

[nemo11]

I'm not sure what you mean by "frictional force increases". Unless you mean that the amount of friction will always be "just enough" to keep it from sliding, up until the point that the force is greater than the maximum available frictional force (Ffmax). Think about this. On a level surface, Ffmax is the greatest, but if there are no external forces trying to slide, then the friction force is zero.

Yes, I mean that the force is always just enough. But how does it happen?

 

[jbriggs444]

Yes, I mean that the force is always just enough. But how does it happen?

How could it be more than enough?

That is, how could the friction that is holding an object in place, keeping it from sliding down an inclined plane force it up the plane instead?

 

[scottdave]

Imagine you have a bookshelf which is designed to withstand 100 pounds of force before breaking. If you put 50 pounds of books on the shelf, how much upward force is the shelf applying to the books? Think about how much they are accelerating.

 

[A.T.]

So my question is how does the friction force increases if N decreases ?

Microscopically contact forces are electromagnetic interactions between atoms, which depend on the distance between them. The relative position of the atoms changes until a force equilibrium is reached, or the static friction breaks.

 

[CWatters]

If you push against a wall the wall also pushes back with "just enough" force to stop you moving.