Static friction confusion -- Friction versus the Normal force

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Discussion Overview

The discussion revolves around the concepts of static friction and the normal force in the context of an inclined plane. Participants explore the relationship between the forces acting on an object at rest on an incline, particularly how changes in the normal force affect the frictional force that prevents sliding.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about how the frictional force can increase when the normal force decreases on an inclined plane.
  • Another participant asserts that friction does not increase in this scenario, suggesting that friction is only "just enough" to prevent sliding until the maximum frictional force is exceeded.
  • There is a reiteration that on a level surface, the maximum frictional force is greatest, but if no external forces are applied, the actual frictional force is zero.
  • A participant questions how friction could exceed the force keeping an object stationary, seeking clarification on the mechanics of frictional force.
  • One participant introduces a metaphor involving a bookshelf to illustrate the concept of forces being "just enough" to maintain equilibrium.
  • Another participant discusses the microscopic nature of contact forces, indicating that they depend on atomic interactions and the distance between atoms.
  • A further analogy is made comparing the interaction of a person pushing against a wall, emphasizing the concept of equal and opposite forces.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the relationship between the normal force and frictional force. Multiple viewpoints are presented, with some participants questioning the mechanics of static friction while others provide analogies to clarify the concept.

Contextual Notes

There are unresolved assumptions regarding the conditions under which static friction operates, particularly in relation to the normal force and external forces acting on the object.

nemo11
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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 ?
 
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It does not .
 
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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.
 
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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.
 
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