Positive or negative work


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Petrina Kan 2I
Posts: 102
Joined: Fri Aug 30, 2019 12:17 am

Positive or negative work

Postby Petrina Kan 2I » Wed Feb 12, 2020 12:43 am

Is work positive when work is done on the system? I am finding varying answers online which is making me confused.

Morgan Carrington 2H
Posts: 54
Joined: Wed Nov 14, 2018 12:22 am

Re: Positive or negative work

Postby Morgan Carrington 2H » Wed Feb 12, 2020 1:17 am

The answer can vary depending on which perspective you are looking at, but when focusing on the system work is positive when work is done on it.

Long Luong 2H
Posts: 51
Joined: Thu Sep 19, 2019 12:16 am

Re: Positive or negative work

Postby Long Luong 2H » Wed Feb 12, 2020 1:27 am

I like to think of a bicycle pump. When you push the pump down, you are exerting a positive force in work on the pump. However, if the gas were to push back against you, it is counteracting your work, so it’s negative work done by the pump (system).

Gurmukhi Bevli 4G
Posts: 49
Joined: Wed Nov 14, 2018 12:20 am

Re: Positive or negative work

Postby Gurmukhi Bevli 4G » Thu Feb 13, 2020 1:27 am

It depends but generally it would be positive when work is being done on the system and negative when the system is performing work on the surroundings

Justin Seok 2A
Posts: 104
Joined: Sat Aug 24, 2019 12:15 am

Re: Positive or negative work

Postby Justin Seok 2A » Thu Feb 13, 2020 2:34 am

When work is done on the system, it is positive, and when the system does work on its surroundings, it is negative.

Connor Chappell 2B
Posts: 59
Joined: Wed Feb 20, 2019 12:16 am

Re: Positive or negative work

Postby Connor Chappell 2B » Thu Feb 13, 2020 8:47 am

When work is done on the system, work is positive. This is due to the fact that the reaction's capacity to do work has INCREASED. The same can be said for a reaction where work is done on the surroundings and the sign is negative because the reaction has lost energy to its surroundings in the form of work.

805373590
Posts: 101
Joined: Wed Sep 11, 2019 12:17 am

Re: Positive or negative work

Postby 805373590 » Thu Feb 13, 2020 8:51 am

When work is done on the system it is positive and when work is done by the system it is negative

aphung1E
Posts: 101
Joined: Sat Aug 24, 2019 12:15 am

Re: Positive or negative work

Postby aphung1E » Thu Feb 13, 2020 8:56 am

I am confused as well especially when utilizing the equation W=-nRT sometimes the solution is positive work instead of negative. How can I tell if it’s negative or positive even if the equation has a negative sign in it?

Max Madrzyk Dis 4G
Posts: 102
Joined: Wed Sep 18, 2019 12:21 am

Re: Positive or negative work

Postby Max Madrzyk Dis 4G » Thu Feb 13, 2020 10:52 am

if you have a system that work is done on then the work of the system will be positive, if you have a system and work is done by it then work of the system will be negative. I think of it as the system is using energy to do some work on the outside so it is losing that energy.

Robin Cadd 1D
Posts: 113
Joined: Thu Jul 11, 2019 12:16 am

Re: Positive or negative work

Postby Robin Cadd 1D » Thu Feb 13, 2020 12:59 pm

If the system does the work, the work is negative.

Eunice Nguyen 4I
Posts: 100
Joined: Sat Aug 17, 2019 12:17 am

Re: Positive or negative work

Postby Eunice Nguyen 4I » Thu Feb 13, 2020 4:31 pm

Work is negative if the system does work on surroundings, while being positive if the surroundings do work on the system.

Anna Heckler 2C
Posts: 102
Joined: Wed Sep 18, 2019 12:18 am

Re: Positive or negative work

Postby Anna Heckler 2C » Thu Feb 13, 2020 4:34 pm

Determining the sign of work is based on what you decide is your system and what is your surroundings - it's relative. Positive work means that work was done on the system, so it gains energy. Negative work means that work was done by the system, and the system loses energy.

504939134
Posts: 103
Joined: Wed Sep 18, 2019 12:21 am

Re: Positive or negative work

Postby 504939134 » Thu Feb 13, 2020 4:36 pm

If you have work being done on the system then work will be positive, and if work is being done by the system then work will be a negative value.

Matthew Tsai 2H
Posts: 101
Joined: Wed Sep 18, 2019 12:20 am

Re: Positive or negative work

Postby Matthew Tsai 2H » Sat Feb 15, 2020 11:48 am

Generally we refer to everything from the perspective of the system, which means that positive work means that work is being done on the system. You can also think of doing work ON some system as adding energy to it, so it makes sense that work is positive.

ramiro_romero
Posts: 90
Joined: Sat Sep 07, 2019 12:16 am

Re: Positive or negative work

Postby ramiro_romero » Thu Mar 12, 2020 10:29 pm

When work is done on the system, it is positive. When work is done by the system onto surroundings, it is negative. If the system exerts force on its surroundings, the system itself loses energy, explaining the negative value.

Joowon Seo 3A
Posts: 100
Joined: Sat Aug 24, 2019 12:17 am

Re: Positive or negative work

Postby Joowon Seo 3A » Fri Mar 13, 2020 6:08 pm

work is positive when it is done on the system. When the system does work, the work is negative.


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