Is Static Friction Capable of Doing Work?

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Discussion Overview

The discussion centers around the question of whether static friction is capable of doing work, exploring various scenarios and definitions related to the concept of work in physics. Participants engage in a technical examination of static friction, displacement, and the implications of different reference frames.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants argue that static friction cannot do work because it involves no displacement between surfaces.
  • Others propose that static friction can be considered to do work in scenarios where there is force transfer without slipping, such as a crate on a truck bed.
  • A participant suggests that the definition of work may allow for interpretations where static friction contributes to work done, depending on how one defines the system and displacement.
  • There is a discussion about the role of static friction as a non-dissipative force and whether it can be viewed as merely transmitting force rather than doing work.
  • Some participants express confusion over the definitions and implications of displacement in relation to static friction and work.
  • A later reply questions the validity of saying that static friction does work, emphasizing that it acts as a connection rather than an energy source.
  • Several participants highlight the importance of specifying the system and reference frame when discussing work and forces.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether static friction can do work, with multiple competing views remaining throughout the discussion.

Contextual Notes

Participants express uncertainty regarding the definitions of displacement and work, and how these relate to static friction. The discussion reveals a dependence on the chosen reference frame and system definitions, which remain unresolved.

  • #31
pixel01 said:
I am not sure if the work done can be a negative value?
In thermaldynamics, the work done is always positive.
Of course work can be negative and that's true in thermo as well!
 
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  • #32
pixel01 said:
This new example is clearer to explain the work done I think.
No, it isn't. It isn't even remotely similar to the other scenarios and does not discuss the same concept. You are now asking if work can be negative, which has nothing to do with whether static friction can cause work to be done.

In any case, the answer to the new question is yes, work can be negative. Work (energy) can either go into or out of a system. Work in is positive, work out is negative. Looking at the net work equation , if the work out is greater than the work in, the net work is negative. http://en.wikipedia.org/wiki/Work_(thermodynamics)#Mathematical_definition
 
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  • #33
In the spring example, at one time, the spring pulls the mass, and the connection does a work. at other time, the mass pulls the spring, the connection should then consume work or does negative work? If we accept that the knot can create work?
 
  • #34
Doc Al said:
Of course work can be negative and that's true in thermo as well!

OK, I should check this first.
 
  • #35
pixel01 said:
In the spring example, at one time, the spring pulls the mass, and the connection does a work. at other time, the mass pulls the spring, the connection should then consume work or does negative work? If we accept that the knot can create work?
You mean the connection between the mass and the spring? Yes, if you didn't know the spring was there, you could say that the knot did work on the mass (+), then the mass did work on the knot (-). [incidentally, if you ignore the spring, now the scenario is pretty much identical to the previous scenario of a string pulling a mass]
 
  • #36
Try this, pixel01 - draw a picture of the system, then draw a circle around the part you want to analyze. For any of these scenarios, knowing how to properly define the system is the key. For the stacked-boxes example, you would draw your circle around the ground, the entire lower box, and part of the upper box - but not the person's finger. That way the only force you are looking at is the force between the boxes and the only motion is between the lower box and the ground.
 
  • #37
Right, the work can be negative and the spring example is meaningless.

Anyway, I am not convinced at the statement: static friction (or string, bolts or nuts...) can do work.
 
  • #38
i think we can say that static friction is capable of doing work in certain frames of reference.
 
  • #39
Not sure how to help you - have you tried drawing a picture?
 
  • #40
pixel01 said:
Right, the work can be negative and the spring example is meaningless.

Anyway, I am not convinced at the statement: static friction (or string, bolts or nuts...) can do work.
Why not?

You have some type of misconception here.
 

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