Kinetic friction and applied force

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Discussion Overview

The discussion revolves around the conditions under which the kinetic coefficient of friction is applied, particularly in relation to static friction and applied forces. Participants explore the nuances of frictional forces in various scenarios, including analogies to other physical phenomena.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the kinetic coefficient of friction is used when the applied force is less than or equal to the static friction force.
  • Another participant suggests that when the applied force equals the static friction force, the net force remains zero, drawing an analogy to the photoelectric effect.
  • It is noted that the kinetic coefficient of friction applies when there is relative motion between surfaces, while static friction is used when there is no relative motion.
  • A participant emphasizes that static friction is relevant even when there is nonzero velocity, provided the object is not sliding on the surface.
  • Clarifications are made regarding the conditions under which kinetic friction is applicable, particularly in relation to net forces and relative motion.

Areas of Agreement / Disagreement

Participants express differing views on the importance of the initial question and the conditions for applying kinetic versus static friction. There is no consensus on the specific conditions under which kinetic friction should be applied, indicating ongoing debate.

Contextual Notes

Participants discuss various scenarios involving friction, but there are unresolved assumptions regarding the definitions of static and kinetic friction, as well as the conditions for their application.

diazdaiz
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I think this question is not important and rarely noticed, but I'm still curious XD
kinetic coefficient of friction is used when the applied force of static friction coefficient is less than than the force that we give, or less than or equal to the force that we give?

sry for my bad english
 
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I think the case would be like the former more. When they are equal the net force is still 0 Newton. (right?)
This situation I think can be analogous to that in photoelectric effect. When the given energy is equal to the work function, there's no electron emitted.
Above is just my ideas.
 
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The kinetic coefficient of friction is used when there is relative motion between the surfaces of contact.
If there is no relative motion between the surfaces of contact, then you don't use kinetic friction.
 
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+1

diazdaiz said:
I think this question is not important and rarely noticed

It is important and noticed.

kinetic coefficient of friction is used when the applied force of static friction coefficient is less than than the force that we give, or less than or equal to the force that we give?

IF static friction is less than the applied force AND that causes the object to slide THEN use the kinetic coefficient of friction.

Normally if the static friction is equal to the applied force the object won't move (it has to be greater for the object to accelerate).

Note that it is usually the net force on an object that determines if it moves. That is not always the same as the applied force.
 
diazdaiz said:
kinetic coefficient of friction is used when the applied force of static friction coefficient is less than than the force that we give, or less than or equal to the force that we give?
even use when net force = friction and v nonzero
 
hackhard said:
even use when net force = friction and v nonzero

It's important to keep in mind that there is kinetic (sliding) friction
when there is a nonzero RELATIVE-velocity (i.e. SLIDING) between the surfaces.

A box sits on rough top of an moving accelerating truck.
Even though the box has nonzero velocity,
if the box is not sliding on the surface of the truck, the friction force on the box in that situation is static friction (not kinetic friction).
 
robphy said:
A box sits on rough top of an moving accelerating truck.
Even though the box has nonzero velocity,
if the box is not sliding on the surface of the truck, the friction force on the box in that situation is static friction (not kinetic friction).
thanks
 

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