Work Equation

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MaryBanh_2K
Posts: 101
Joined: Wed Sep 18, 2019 12:21 am

Work Equation

Postby MaryBanh_2K » Wed Jan 29, 2020 9:40 pm

What is the conceptual significance of having the negative sign in the equation: w=-(external pressure) x (change in volume)?

Ariel Davydov 1C
Posts: 110
Joined: Thu Jul 11, 2019 12:16 am
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Re: Work Equation

Postby Ariel Davydov 1C » Wed Jan 29, 2020 9:48 pm

It is to accommodate for the sign of the change in volume. If work is being done on the system (meaning work is positive), the volume of the system will decrease (ex: piston being pushed in) and the change in volume will be negative. Without the negative in front of the equation to counterbalance the negative change in volume, you would obtain a negative value for work done instead of a positive one. Hope this helps!

Pegah Nasseri 1K
Posts: 100
Joined: Wed Feb 27, 2019 12:15 am

Re: Work Equation

Postby Pegah Nasseri 1K » Fri Jan 31, 2020 12:05 am

When work is done by the system, the system will lose energy to its surroundings. The negative sign in the equation w = - (P * delta V) accounts for this loss of energy by the system when it performs work. Negative work is performed by the system when the volume increases or expands at constant pressure. Positive work is performed by the system when the volume is compressed at constant pressure.

705121606
Posts: 68
Joined: Wed Sep 18, 2019 12:17 am

Re: Work Equation

Postby 705121606 » Fri Jan 31, 2020 3:52 pm

When it is being compressed and volume is decreasing then work done on the gas/system is positive and gas done by the system is positive. When there is an expansion there is negative work done on the gas and positive work done by the gas.


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