Work sign
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Work sign
I keep getting confused on how to determine whether the sign for work is negative or positive. I know it has to do with whether we do work on the system or on the surrounding. How do we determine this again?
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Re: Work sign
If the system is doing work (work done by system), the work sign is negative. If work is being done on the system, the work sign is positive. When work is done on the system, it is the surroundings that do the work. Hope that helps!
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Re: Work sign
I agree with the comments above, and also work of expansion would be negative because there is an increase in volume do to work being done by the system. In contrast, work of compression is being done on the system since there is a decrease in volume by some external force/pressure.
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Re: Work sign
If work is done on a system, the value is positive (think of an increase in internal energy). If a system does work, the value of w is negative (think of a decrease in internal energy). I hope this helps!
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Re: Work sign
If the system is the one doing the work, then it will have a negative sign in front of it. However, if work is being performed on the system then, work will be positive.
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Re: Work sign
You have to determine the parts that make up the system and differentiate these parts from the surrounding. Work done on the system is positive, the system does not actually exert any work. However, work is negative if this system exerts work on the surrounding.
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Re: Work sign
When a gas is doing work, it is a -w. When the surroundings are doing work on a system, it is +w because the system is gaining work.
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Re: Work sign
Work done ON a system is positive (i.e. the system is gaining something). Work done BY a system is negative (i.e. the system is losing something).
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Re: Work sign
Work done BY the system (the system does work) is negative. Work done ON the system is positive.
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Re: Work sign
When a system does work (like pushing a piston to expand the volume), it is losing energy, so the value of work is negative.
When a system has work done on it (like compression), it is gaining energy, so the value of work is positive.
When a system has work done on it (like compression), it is gaining energy, so the value of work is positive.
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Re: Work sign
When work is done on a system it is positive. So when a system is compressed, work done on the system is positive. When the system expands, work is negative because the system is doing work against the surroundings.
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Re: Work sign
Think of the bicycle example from lecture. If we push air into bike, we are doing the work and the bike is gaining work.
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Re: Work sign
When a system does work, work is negative. If the system has negative work, the surroundings should have positive work. When work is being done on a system, work is positive. If the system has positive work, the surroundings should have negative work.
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Re: Work sign
When a problem says that compression occurs on a system I think of the work as positive as the surroundings are doing work on the system. So, when expansion occurs work would be negative since it's the system this time doing the work by expanding.
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Re: Work sign
If work is done by the system, it's negative. If work is done on the system, it's positive.
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Re: Work sign
When the work is done by the system on the surroundings, w will be negative, since the system is losing energy by doing work. And when work is done on the system by the surroundings, w will be positive, since the system is gaining energy from the surroundings.
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Re: Work sign
It is important to first determine and define the system in the scenario. Then, once the system is defined, then work is negative when the system does work. If work is done on the system, then the sign of work would be positive.
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Re: Work sign
when work is done ON the system the value will be positive and when work is done BY the system it is a negative value. When positive, the system is being compressed and when work is negative the system is expanding. Usually, in the problem it mentions that the system is doing work, which means that the system is losing energy so it would be a negative.
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Re: Work sign
If work in done on the system, work is positive, if it is done by the system, work is negative. You can think about it like if a system is doing work it is losing energy, so w is negative.
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Re: Work sign
If the work is done by the system it is negative, if the work is done by the surroundings/ on the system it is positive.
Re: Work sign
To answer your question, work done BY the system is negative, and work done ON the system is positive. The way I like to think about it is when the system does work, it needs to use energy to do that work so it ends up losing energy. When work is done by the surroundings on the system, I think that the surroundings lose energy and give it to the system (because of conservation of energy), ultimately increasing the system's energy. Hope this helps
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Re: Work sign
When the system is doing work, work is negative. On the other hand, when the work is done on the system, work is positive.
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Re: Work sign
if work is done on the system then the sign is positive, if work is done by the system then it's negative!
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Re: Work sign
Hi,
When work is done by the system, work is a negative value. The way you can think of this is that when work is done by the system, it means that the system is dong work and, in doing so, it's losing energy. Therefore, work is negative.
When work is done on the system, work is a positive value. Again, thinking about this in terms of energy, since work is being done on the system, there is an input of energy from surroundings into the system, which results in work being positive.
Also, it's worth to mention that when the system expands (that is, the system does work of expansion), work is negative, and when it is compressed, work is positive.
Hope this helps :)
When work is done by the system, work is a negative value. The way you can think of this is that when work is done by the system, it means that the system is dong work and, in doing so, it's losing energy. Therefore, work is negative.
When work is done on the system, work is a positive value. Again, thinking about this in terms of energy, since work is being done on the system, there is an input of energy from surroundings into the system, which results in work being positive.
Also, it's worth to mention that when the system expands (that is, the system does work of expansion), work is negative, and when it is compressed, work is positive.
Hope this helps :)
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Re: Work sign
You can also think of gas compressions and expansions. If a gas is being compressed, volume goes down and the surroundings are doing work on the system and so work is positive. If a gas is being expanded, then the volume is increasing and the system is doing work to the surroundings, thus making it negative. In chemistry we always think of work in terms of the system, whereas in physics it is in terms of the surroundings!
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Re: Work sign
I like to think of it this way:
If the system is performing work (expanding against an external pressure, for example) - the system is "losing" some of its capacity to do work - and the sign of work should be negative
If work is being performed on the system (compression against an internal pressure, for example) - the system is "gaining" more capacity to do work - and the sign of work should be positive.
If the system is performing work (expanding against an external pressure, for example) - the system is "losing" some of its capacity to do work - and the sign of work should be negative
If work is being performed on the system (compression against an internal pressure, for example) - the system is "gaining" more capacity to do work - and the sign of work should be positive.
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Re: Work sign
If work is done on the system then work is positive but if the system is doing work then work is negative
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Re: Work sign
Work done by the system is negative and when work is done on the system it is positive. I think of it as when you’re working out you’re tired after because you’re using energy, and after you get a massage or something you have more energy and you’re more relax. Hopefully this makes sense
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Re: Work sign
Hi! The work done by a system is negative, whereas the work done on a system is positive.
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Re: Work sign
When work is positive that means work is being done by the system. When work is negative that means work is done on the system.
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Re: Work sign
If work is done by the system then the value for work will be negative. If work is done on the system then the value for work will be positive.
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Re: Work sign
Work done by the system is negative and work done on the system is positive. When a system does work, it is losing energy, thus the sign is negative. When work is being done on the system there is energy being transferred to it, making the work of the system positive.
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Re: Work sign
The sign of work is deoendent on who does work and who gets work done on them. If the system has done work then it's the normal negative. Therefore, if the system gets work done on it then work is positive.
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Re: Work sign
If the system itself is doing work, then it is negative. If work is being done onto the system, then it should be positive.
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Re: Work sign
Hi! A negative sign would indicate that work is being done by the system, while a positive sign would indicate work is being done on the system.
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Re: Work sign
Because the system is our reference point, if it is doing work, we say that it is losing energy, which is why work done by the system has a negative sign.
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Re: Work sign
It depends on which way the work is done. If work is done ON the system, then work would be POSITIVE. If work is being done BY the system, then work would be NEGATIVE since the system is exerting energy onto the surroundings by doing the work.
Compression of a system usually means work is being done on the system, so it would be positive. Expansion of the system indicates work being exerted onto the surroundings, so work should be negative.
Compression of a system usually means work is being done on the system, so it would be positive. Expansion of the system indicates work being exerted onto the surroundings, so work should be negative.
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Re: Work sign
I think of it as because ability for work done by the system is limited based on capacity, any work done by the system is negative (expended) whereas any work done to the system is a sort of input so it is positive
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Re: Work sign
If the system is doing the work, then the sign is negative. If work is being done on the system, then the sign is positive.
Re: Work sign
If the system is doing work then the sign is negative, but if work is being done then it is positive.
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