During lecture, Dr. Lavelle gave the example that compressing a piston is doing work on the system and the piston moving out is the system doing work on the surroundings.
Other than the movement of pistons, are there other examples or ways in which work can be done on a system? What are other ways/examples in which a system is doing work on the surroundings?
Doing Work on the System
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Re: Doing Work on the System
Work deals with the transfer of energy, and w is negative when energy leaves the system and positive when energy enters the system. Another example of work might be if heat from the system is escaping to the surroundings.
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Re: Doing Work on the System
When work is done on the system, work is positive since the system gains energy as the external surroundings are expending energy and putting work into the system (i.e. a bicycle pump compressing the air). However, when work is done BY the system, work is negative since the system loses energy by performing work onto the surrounding environment (i.e. balloon expanding and increasing in volume). I hope this helps!
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Re: Doing Work on the System
Looking at the equation for the w term, anytime you get a negative value for deltaV (compressing, like what a piston does) the work increases. A positive deltaV translates into work being used up and lost. A coiled up spring can push something further than a completely expanded spring. You could increase the potential energy and the ability of the spring to do work by squeezing it.
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Re: Doing Work on the System
In regards to gases, work can be done on any system where the volume isn't constant. So if you have a chemical reaction in an open beaker where moles of gas are created, work is done because these new moles of gas push on the other gas molecules to make space for themselves. The reason a piston system is useful is because it allows you to see these gas molecules applying this force over a distance as you can see the piston expanding as the gas molecules push on it.
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Re: Doing Work on the System
Another example could be a bike pump. Work is being done on the system when the pump is pushed down and the system is compressed. Overall, work is being done on a system when energy is being used on it.
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