Question about the significance of negative work

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Discussion Overview

The discussion revolves around the concept of negative work in physics, particularly its significance and implications in the context of the work-kinetic energy theorem. Participants explore the relationship between work done by an object and the work done on that object, as well as the interpretation of negative values in scalar quantities.

Discussion Character

  • Conceptual clarification, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions the significance of negative work and its physical implications, particularly in relation to the work-kinetic energy theorem.
  • Another participant agrees with the initial claim, stating that negative work indicates energy being taken from the object, and clarifies that scalars can be negative but lack direction.
  • A later reply reiterates the equivalence of work done by two objects, suggesting that if object A does work W on object B, then object B does work -W on object A.

Areas of Agreement / Disagreement

Participants generally agree on the interpretation of negative work and its implications, but the discussion includes some exploration of the underlying concepts and potential confusion surrounding scalar quantities.

Contextual Notes

Some assumptions about the definitions of work and energy may not be fully articulated, and the discussion does not resolve all potential confusions regarding the interpretation of negative values in scalar quantities.

Bipolarity
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I am having some trouble understanding the significance of negative work.

If the work that I do on object X is W, is it equivalent to saying that object X does work on me equal to -W ?

After all, work is scalar, so I can't fathom the physical significance of negative work.

Also, according to the work-kinetic energy theorem, due to the way in which work and kinetic energy are both defined, when I do work W on an object X, its kinetic energy increases by W and my energy decreases by W. Isn't that equivalent to saying that the object did work of -W on me, since at least in terms of kinetic energy the two are equivalent?

All help on my understanding of this concept is appreciated.

BiP
 
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Yes, what you stated is correct. The object does negative work on you. In a sense, the negative means that energy has been taken FROM the object in question (aka you). Remember, scalars can be negative! They just can't have direction. You might be confused because people in the early stages of physics courses will say that speed is a scalar and velocity is a vector, the former being unable to be positive, but this is specifically because of the way speed is defined; it is not a general property of scalars. I assume this is where the confusion lays?
 
Pengwuino said:
Yes, what you stated is correct. The object does negative work on you. In a sense, the negative means that energy has been taken FROM the object in question (aka you). Remember, scalars can be negative! They just can't have direction. You might be confused because people in the early stages of physics courses will say that speed is a scalar and velocity is a vector, the former being unable to be positive, but this is specifically because of the way speed is defined; it is not a general property of scalars. I assume this is where the confusion lays?

OK I get it so far. So if object A does work W on object B, then that is perfectly equivalent to saying that object B does work -W on object A?

BiP
 
That is correct.
 

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