Static friction confusion -- Friction versus the Normal force

• nemo11
In summary: In the same way, the atoms on an inclined plane will create just enough friction to keep the object from sliding down.So my question is how does the friction force increases if N decreases ?The friction force on an inclined plane is always just enough to keep the object from sliding down, as long as the angle of inclination is not too steep.
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 ?

Last edited by a moderator:
It does not .

DLeuPel
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.

scottdave said:
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?

nemo11 said:
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?

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.

jbriggs444
nemo11 said:
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.

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

jbriggs444

What is static friction?

Static friction is the force that resists the motion of an object when it is in contact with another object. It acts in the opposite direction of the applied force and prevents the object from moving.

What is the difference between friction and normal force?

Friction is a force that acts in the opposite direction of motion and resists the movement of an object, while normal force is a force that acts perpendicular to the surface of contact between two objects. In the case of static friction, both forces work together to prevent an object from moving.

How is static friction different from kinetic friction?

Static friction occurs when there is no relative motion between two objects, while kinetic friction occurs when there is relative motion between two objects. Static friction is usually greater than kinetic friction, as it requires more force to overcome the initial resistance of an object at rest.

How does the weight of an object affect static friction?

The weight of an object does not directly affect static friction. However, the normal force, which is equal to the weight of an object in a stable equilibrium, does affect the amount of static friction. The greater the normal force, the greater the maximum possible static friction force.

What factors can affect the amount of static friction?

The amount of static friction can be affected by the type of surfaces in contact, the roughness of the surfaces, and the amount of force applied. It can also be affected by the presence of lubricants or other substances between the two surfaces.

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