## Examples of work being done

$\Delta U=q+w$

Angela 1K
Posts: 80
Joined: Fri Sep 29, 2017 7:05 am

### Examples of work being done

What are some examples in which work is being done on a system?

In an example where volume and pressure both change, is work still being done on the system?

In a system that expands against a vacuum, is work being done?

Shawn Patel 1I
Posts: 54
Joined: Thu Jul 27, 2017 3:01 am

### Re: Examples of work being done

Hey,
An example of a system doing work would be when a gas is pushing against a piston. When volume and pressure are changing, there can be work being done on the system. If there is a vacuum, work cannot be done because there is nothing to do work against.

Posts: 54
Joined: Thu Jul 27, 2017 3:00 am
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### Re: Examples of work being done

Yes what Shawn said above is true. Just to add on, a system does no expansion work when it expands into a vacuum, because there is no opposing force. Expansion work against zero work is called free expansion.

Yu Chong 2H
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

### Re: Examples of work being done

I think that for the purpose of our class, we can think of work done by a system to be a force pushing against the system. If it's a gas, the work done on a system will most likely cause a contraction of the gas.

204932558
Posts: 23
Joined: Fri Sep 29, 2017 7:05 am

### Re: Examples of work being done

If gas expands against vacuum no work is being done because the external pressure is zero. An example of work done on a system would be a piston compressing the gas inside a column. Work is done on the gas.

Justin Folk 3I
Posts: 43
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Examples of work being done

For example pushing a cart is work being done. You use some energy (instead of to heat up) to push the cart.

Oscar Valdovinos 1I
Posts: 29
Joined: Fri Sep 29, 2017 7:05 am

### Re: Examples of work being done

Another aspect of work to note is that work is not a state meaning that its value depends on the path taken. A quick example of this would be pushing a ball 100ft on a flat surface would require less work on the system than pushing that same ball uphill for a 100ft.

Jaewoo Jo 2L
Posts: 31
Joined: Fri Sep 29, 2017 7:06 am

### Re: Examples of work being done

since work is force x distance, doing anything that requires a certain force to move something a certain distance (like push-starting a car) is work being done.