8.3 Homework


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Vanessa Romero-Campos 2B
Posts: 39
Joined: Fri Sep 25, 2015 3:00 am

8.3 Homework

Postby Vanessa Romero-Campos 2B » Wed Jan 17, 2018 11:17 pm

Can someone explain why work on air is positive when an air bicycle pump is compressed .
I thought work is positive if work is done by the system, and negative if work is done on the system. Wouldn't work be done on air, so it'd be negative?

Rachel Lu_dis1H
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Joined: Fri Sep 29, 2017 7:06 am
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Re: 8.3 Homework

Postby Rachel Lu_dis1H » Wed Jan 17, 2018 11:21 pm

In chemistry, work is negative when it is done by the system. When work is done on the system it is positive. (In physics it is the opposite) So since work is being on the system (air) it is positive.

skalvakota2H
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Joined: Sat Jul 22, 2017 3:01 am

Re: 8.3 Homework

Postby skalvakota2H » Wed Jan 17, 2018 11:30 pm

Consider how work is equal to -P∆V. The change in volume of the pump is negative since the pump is being depressed. So algebraically, when substituting a negative value for deltaV, the sign for work will be positive, hence implying that work is being done. Conceptually, the work is positive because with respect to air, work is being done on the air since it is being depressed.

Clarisse Wikstrom 1H
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Re: 8.3 Homework

Postby Clarisse Wikstrom 1H » Wed Jan 17, 2018 11:33 pm

The work is done TO the system, since the outside pressure pushes the piston down causing the compression. Because the system doesn't have to do any work, therefore the work on the interior air is positive.

IF the piston moved out to increase the volume inside, then the system would be DOING the work and the work on the interior air would be negative.

Yeyang Zu 2J
Posts: 58
Joined: Fri Sep 29, 2017 7:06 am

Re: 8.3 Homework

Postby Yeyang Zu 2J » Fri Jan 19, 2018 4:04 am

the truth is totally opposite.
when work is done by the system, w is negative (expand
when work is done by the environment to the system, w is positive (compress


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