Negative and positive work - Question

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    Negative Positive Work
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Discussion Overview

The discussion revolves around the concept of work in physics, specifically focusing on the conditions under which positive or negative work is done on an object. Participants explore scenarios involving forces applied to a mass moving upward while experiencing different accelerations and displacements.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether they are doing positive work while applying a force that accelerates a mass upward, despite the mass accelerating downward.
  • Another participant asserts that work depends on the sign of the force and the displacement, indicating that changing the sign of either affects the work done.
  • A participant further clarifies that their force is in the same direction as the displacement, suggesting they are doing positive work, even if the mass is slowing down.
  • Another response confirms that the participant is indeed doing positive work on the object, while noting that the Earth is doing negative work, leading to a negative net work done on the mass.

Areas of Agreement / Disagreement

Participants express differing views on the conditions for positive work, with some agreeing that the participant's force can still result in positive work despite the mass slowing down, while others emphasize the importance of net forces in determining overall work.

Contextual Notes

There are unresolved aspects regarding the definitions of work and the conditions under which it is considered positive or negative, particularly in relation to net forces and individual contributions.

Who May Find This Useful

This discussion may be useful for students and educators in physics, particularly those interested in the concepts of work, force, and motion in mechanics.

SigmaScheme
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I accelerate a mass upward by 2G (2×force of gravity) over some change in height Δh_{1}, then I apply only \frac{1}{2}G over some other change in height Δh_{2}.

If, over Δh_{2}, the mass still moving upward (but accelerating downwards), am I doing positive work over Δh_{2} even though the mass is accelerating in the opposite direction to the force I am applying?THANKS!
 
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No-- the work depends on the sign of the force (and so the acceleration), times the sign of the displacement. So switching the sign of one or the other (but not both) will change the sign of the work.
 
OK, thanks, So what about MY work alone due to the force I am applying, rather than the work due to the net force.

MY force and x ARE in the same direction (although the mass is slowing down). Splitting the question into components, am I alone doing positive work regardless of net work - even though the mass is slowing down?
 
SigmaScheme said:
am I alone doing positive work regardless of net work - even though the mass is slowing down?
Yes, you are still doing positive work on the object. The Earth is doing negative work. And the net work done on it is negative.
 

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