Regarding the definition of Work

In summary, there seems to be a discrepancy between the notation used in AP Physics and most textbooks when it comes to the sign of work done by a gas during expansion. AP Physics states that negative work is done, while most textbooks say it is positive. However, it is just a convention and the important thing is to understand the meaning of the signs in the equations. In this case, the first law of thermodynamics states that Q12-W12 equals the change in energy (ΔE) and W12 represents the work done by the gas. So, the work done by the gas is considered positive when it expands.
  • #1
Abelard
31
0
Confuses me very much. AP Physics specifies that when gas expands, negative work has been done. But most textbooks say that it's positive work.

Could anyone explain the discrepancy here?
 
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  • #2
It's usually a convention that is used.

Normally, when a gas expands, you would say that the gas is doing work

if the gas contracts, you would say that work is being done on the gas.
 
  • #3
I was worried about the sign when the gas expands. Why do AP and textbooks differ in signs?
 
  • #4
Abelard said:
I was worried about the sign when the gas expands. Why do AP and textbooks differ in signs?

Not too sure, but you just need to know what the signs mean in the equations.

e.g. first law of thermo dynamics

Q12-W12= ΔE

W12 happens to be the work done by the gas
 
  • #5
Thanks a lot though. So the work done by the gas is positive when it expands.
 
  • #6
Abelard said:
Thanks a lot though. So the work done by the gas is positive when it expands.

Yep, that's the normal convention used.
 

1. What is the definition of work in science?

The scientific definition of work is the transfer of energy from one object to another by applying a force over a distance. In simpler terms, work is done when a force causes an object to move.

2. What is the unit of measurement for work?

The unit of measurement for work is the joule (J). This unit is equivalent to one newton-meter (N∙m) and is named after the English physicist James Prescott Joule.

3. How is work related to energy?

Work and energy are closely related concepts in science. Work is the process of transferring energy, and the amount of work done on an object is equal to the change in its energy. This relationship is described by the work-energy theorem: W = ΔE, where W is work, and ΔE is the change in energy.

4. Can negative work be done?

Yes, negative work can be done. This occurs when the force applied to an object is in the opposite direction of its motion. Negative work results in a decrease in the object's energy, and it is often associated with friction or other forms of resistance.

5. How is work calculated?

Work is calculated by multiplying the force applied to an object by the distance it moves in the direction of the force. The formula for work is W = Fd, where W is work, F is force, and d is distance. This formula can be used for both positive and negative work.

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