Work Done by Gravity - Positive or Negative

Click For Summary
SUMMARY

The discussion centers on the concept of work done by gravity, specifically addressing whether it is positive or negative. Participants clarify that work is defined as the product of force and displacement, expressed mathematically as Work = Force x Displacement. When the force and displacement are in the same direction, work is positive; conversely, when they are in opposite directions, work is negative. The consensus is that work done against gravity (e.g., lifting an object) is negative, while work done with gravity (e.g., dropping an object) is positive.

PREREQUISITES
  • Understanding of basic physics concepts, particularly work and energy.
  • Familiarity with the equation Work = Force x Displacement.
  • Knowledge of force direction and displacement in physics.
  • Basic grasp of sign conventions in physics.
NEXT STEPS
  • Study the implications of work-energy theorem in physics.
  • Learn about different forces and their effects on work, including friction and tension.
  • Explore gravitational potential energy and its relationship with work done by gravity.
  • Investigate real-world applications of work calculations in engineering and physics.
USEFUL FOR

Students studying physics, educators teaching mechanics, and anyone interested in understanding the principles of work and energy in physical systems.

axer
Messages
35
Reaction score
4

Homework Statement


UZofJHBRR5KS8VwVle6pNA.png


Homework Equations

The Attempt at a Solution


I first said it's B, since force throws up = positive.
gravity down= also positive, please help asap thanks
 

Attachments

  • UZofJHBRR5KS8VwVle6pNA.png
    UZofJHBRR5KS8VwVle6pNA.png
    44.7 KB · Views: 1,288
Physics news on Phys.org
What's the definition of the work done by a force? What determines whether that work is positive or negative?

(Is this thread mistitled?)
 
Doc Al said:
What's the definition of the work done by a force? What determines whether that work is positive or negative?

(Is this thread mistitled?)
OOps yeah it is, ill change it. D: if the displacement in the same direction as force then there is work, so going down is 100% positive.

But going up is tricky.EDIT: i can't edit it.
 
axer said:
if the displacement in the same direction as force then there is work
Careful. Work is done even if they are in opposite directions. But the sign is different.

axer said:
so going down is 100% positive.
RIght, because force and displacement are in the same direction.

axer said:
But going up is tricky.
It shouldn't be. :)

axer said:
EDIT: i can't edit it.
Done.
 
Doc Al said:
Careful. Work is done even if they are in opposite directions. But the sign is different.RIght, because force and displacement are in the same direction.It shouldn't be. :)Done.
so the work going up is negative, since gravity pulls down and displacement is going up.?
 
axer said:
so the work going up is negative, since gravity pulls down and displacement is going up.?
Exactly.

Work = Force x Displacement. No matter what sign convention you use, when the force and displacement are in the same direction, work is positive; when opposite, work is negative. (Try it and see.)
 
Doc Al said:
Exactly.

Work = Force x Displacement. No matter what sign convention you use, when the force and displacement are in the same direction, work is positive; when opposite, work is negative. (Try it and see.)
thanks, you're a life saver.
 

Similar threads

Confusion over acceleration of gravity as positive/negative
  • · Replies 10 ·
Replies
10
Views
2K
Work done by a force down a ramp
  • · Replies 11 ·
Replies
11
Views
2K
How can "work" done by a force be negative?
  • · Replies 19 ·
Replies
19
Views
1K
Thermodynamic Work vs Mechanical Work
  • · Replies 3 ·
Replies
3
Views
1K
Why Is Work Positive When Done Against the Electric Field?
  • · Replies 22 ·
Replies
22
Views
4K
Work Pulley Problem with constant speed
  • · Replies 2 ·
Replies
2
Views
1K
Misunderstanding Work-energy theorem and center of mass properties
  • · Replies 7 ·
Replies
7
Views
2K
Sign conventions for work done by/on a system
  • · Replies 9 ·
Replies
9
Views
4K
Why Did My Torque Sign Change in Rotational Equilibrium?
  • · Replies 9 ·
Replies
9
Views
1K
Work done in elevator problem — is it positive or negative?
  • · Replies 3 ·
Replies
3
Views
3K