What Causes Negative Work in Physics?

  • Context: High School 
  • Thread starter Thread starter Ellipses
  • Start date Start date
  • Tags Tags
    Negative Work
Click For Summary

Discussion Overview

The discussion revolves around the concept of negative work in physics, specifically addressing the conditions under which work is considered to be done and how negative work can occur. Participants explore theoretical aspects and clarify definitions related to work and force in the context of physics.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the conditions for work, particularly how negative work can occur if force and displacement are in opposite directions.
  • Another participant suggests rewording the condition regarding work to indicate that the force must not be perpendicular to the displacement, allowing for both positive and negative work depending on the direction of the force relative to displacement.
  • A third participant reiterates the idea that work is done when the displacement is either in the same or opposite direction to the force, clarifying that negative work occurs when the displacement is opposite to the force.
  • Another participant states that work can either impart energy to a system (positive work) or extract energy from it (negative work), emphasizing the dual nature of work in terms of energy transfer.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the wording of the conditions for work and how to best understand negative work. Multiple competing views on the definitions and implications of work remain present in the discussion.

Contextual Notes

There are unresolved nuances regarding the definitions of work and the conditions under which it is considered positive or negative, as well as the implications of force direction relative to displacement.

Ellipses
Messages
17
Reaction score
0
Hello everyone.

I understand the concept of work in general, but the concept of negative work still somewhat baffles me. One of my main problems is this: according to my textbook, 3 conditions must be met in order for work to be done, and one of them is "at least part of the force must be in the same direction as the displacement."

Well, how can negative work occur if the force in displacement are going in opposite directions?

Thanks for the help!
 
Physics news on Phys.org
That's a poorly worded condition. I would reword it to say that in order for work to be done, the force must not be normal to the displacement (in other words, the dot product of the force and displacement must be nonzero). It can be in the same direction as the displacement or the opposite direction, so long as it isn't directly perpendicular.
 
Ellipses said:
Hello everyone.

I understand the concept of work in general, but the concept of negative work still somewhat baffles me. One of my main problems is this: according to my textbook, 3 conditions must be met in order for work to be done, and one of them is "at least part of the force must be in the same direction as the displacement."

Well, how can negative work occur if the force in displacement are going in opposite directions?

Thanks for the help!

As has been said, that's not correct. Imagine a force directed in a certain direction and label that direction with an arrow. If the displacement is a 90 degree angle from that arrow (perpendicular) than no work is done. However, if the displacement is, at least a little bit, pointing along OR OPPOSITE to the force arrow than work is done. In the opposite direction case that work is negative. Intuitively you can say that this force is giving energy BACK to the system.
 
Work is done by a particular force. This can be either done by imparting energy to the system or by extracting energy from the system. The former case we say the work done is positive and the latter it is negative.
 

Similar threads

Undergrad Why the work done is coming out to be positive?
  • · Replies 9 ·
Replies
9
Views
2K
Undergrad Positive and negative work in terms of energy.
  • · Replies 6 ·
Replies
6
Views
6K
High School Work Done By Conservative Forces
  • · Replies 1 ·
Replies
1
Views
2K
High School How does an object gain potential energy?
  • · Replies 54 ·
2
Replies
54
Views
7K
Undergrad Physics C: Mechanics - Negative Energy and Potential Energy Curves
  • · Replies 5 ·
Replies
5
Views
3K
High School Curious about the work - energy theorem
  • · Replies 8 ·
Replies
8
Views
2K
High School Curious about Work and Energy Consumption
  • · Replies 8 ·
Replies
8
Views
2K
High School Work-Kinetic and Work-Potential theorems relation
  • · Replies 4 ·
Replies
4
Views
2K
High School What is the need for the concepts of Work and Energy (KE)?
  • · Replies 8 ·
Replies
8
Views
2K
High School Conceptually understanding change in potential energy with 0 net work
  • · Replies 9 ·
Replies
9
Views
2K