Work (Positive/Negative)?

[Justin An 2L]

When work is negative, does that mean work is done on the system (and therefore energy is added to the system) or is it the other way around?

[Furkan Acar 3C]

Well a negative sign in work means that system itself actually lost energy, or at least that's how I remember learning it. In fact, theres another post that has an answer like this:

"The negative sign means that the system (i.e., the reaction) lost energy. In order for a system to be able to do work it must be able to provide energy to do that work and therefore must be able to give off energy (i.e., a negative value)."

Hope this helps.

[Justin An 2L]

I think I'm just getting confused by the terminology of work done on vs. work done by... are they the same thing?

[Rachel Chan 1B]

I believe it's the other way around. I think of it as this: when work is negative, work/energy is leaving the system and being used on the surroundings. When work is positive, it is being done on/added to the system by the surroundings.

As for your second question, unfortunately it depends! But the phrases are opposites, so if work is done on the system, it is the same as work done by the surroundings. If work is done on the surroundings, it is work done by the system. It's kinda like a zero-sum/seesaw.

[605607825]

Hello!
Work will be negative when work is done by a system.The negative sign tells us that energy is lost and in order for a system to do work, it has to be able to provide energy. If work is positive,it is being added to the system. If work is being done on a system, the same amount is done by its surroundings. When work is done on a system, the energy that is released will be absorbed by the system so work will be positive. I hope this helped!

[Nicole Weinstein 3E]

Work is negative when it loses energy to its surroundings through expansion. Dr. Lavelle used a good example in lecture of using a bike pump where if we put energy into pushing the pump, we are losing energy. Conversely, work is positive when it gains energy through compression. The surroundings are putting their energy into the system so its a net gain.

[Kimia Rategh 2A]

Hi! Just adding on to what others have said here, but when the value of work is negative, that means that work is being done by the system. What I find helpful in remembering this is using the equation w=-p∆V. When ∆V is positive, meaning the system is expanding which it does so by pushing against itself to expand, then work would be negative. Therefore it would make sense that if the work is negative that means that the system is doing work. Conversely, if work is positive that means work is being done to the system. Again when work is being done to the system, that means it is compressing, which would mean some outside force is pushing down on it and ∆V would be negative since Vf is smaller than Vi. Therefore using the equation -p∆V with a -∆V, we would have positive work. Hope this helps!

[Martha Avila 1I]

Hello. So when work is negative this means that work is done by a system. When work is positive this means that work is done on a system. It can be confusing at times but I hope this helps.

[Joellen 1B]

When work is negative, this means that work is done by the system since it is losing energy. When it is positive, work is being done on the system.

[Anika Scott 3A]

It depends on the context of the work. Work done by the system is opposite to work done on the system. Work done by the system is negative because the system is using, thus losing energy.

[Jessica Cornelia Hongarta 1G]

When work is negative, it means that work is done by the system (the system uses/loses that energy to do work). So, when work is done on the system, work is positive (since the surrounding is the one doing the work/losing energy).

Hope this helps!

[gwenkelley3L]

If work is negative, this means that the work is being done by the system, and therefore the system is losing energy, however if the work is positive, it is being done to the system and therefore the system is gaining energy!

[Dillon Taing 3H]

When considering how the energy of a system changes, the sign of the work value is dependent on which direction the mechanical energy is being transferred. If work energy is being done by the system, then the sign convention will be negative, while if work energy is done on the system, the sign convention will be positive.

[Xzandalyn Kallstrom 2C]

I think about it this way:
If the sign is NEGATIVE the system is doing work on the surroundings, essentially expelling energy, or transferring energy from the system to the surroundings.
If the sign is positive, the system is absorbing energy. That means it takes energy from the surroundings and it goes into the system.

[Preethika Praveen 2G]

When work is done on a system, energy is added to the system, and work is positive. When work is being done by the system, energy is being used by the system so work would be negative.

[Celine_Nguyen_3K]

The work value is negative when work is being done by the system because the system is losing energy (transferring energy from the system to the surroundings) in order to do that work. The work value is positive when work is being done on the system because the energy is being transferred from the surroundings to the system, so the system gains a positive work value.

[Bela Patel 2B]

When work is positive, that means work is being done ON the system and if work is negative, that means work is being done BY the system.

[Nomi Heidari-Bateni 2K]

When work is done on the system, w is positive. When the system does work, then w is negative. I remember this because delta H has positive and negative signs in a similar manner. When the heat is released (the system puts heat out into the surroundings), delta H is negative. When the heat is absorbed (surroundings puts heat on the system), delta H is positive.

[Terrence Chi]

Hi, the negative work value means that the system lost energy whereas the positive work value means work is done on the system and gains energy. Hope this helps!

[Jaipal Virdi 2I]

Work done by the system is negative (Internal energy deceases)
Work done on the system is positive (Internal energy increases).

[Diana Avalos]

-w = work done by the system
+w = work done on the system

[Mark_Botros_1D]

Furthermore, to add to the discussion, if work is done on the system, work will contribute to increasing internal energy. However, if work is done by the system, such work will contribute to decreasing internal energy.

[Hannah Thornton 1F]

Work is negative when work is done by the solution, since the system needs to use its energy to do its work and therefore energy is lost, hence the negative sign. Positive work would be work done on a system since energy is being added to it.

[Hannah Thornton 1F]

Work is negative when work is done by the solution, since the system needs to use its energy to do its work and therefore energy is lost, hence the negative sign. Positive work would be work done on a system since energy is being added to it.

[Achyutha Kodavatikanti_3H]

work done by the system on its surroundings is negative (expansion, for example). work done on the system by its surroundings is positive (compression, for example).

[Chelsea Tran 3H]

I believe work is negative when the system is doing work (losing energy) and positive when work is being done onto the system (gaining energy).

[Chris Van 2J]

A negative work is when the system is doing the work and losing energy while work being done on the system is positive.

[HemangD 3K]

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

[Lauren Wasef 3C]

+ when work is done ON the system. - when work is done BY the system.

[Daniel Tabibian 3K]

If work is negative then energy is leaving the system and therefore the system is doing work on its surroundings.

[Ameerah Hameed 3B]

When work is done on the system it is positive, and when work is done by the system it is classified as negative.

[Lauren Brotman 2F]

When work is done by the system, the system loses energy by achieving motion against an opposite force. For example, a system expanding against external pressure is doing work. So, when a system does work, its negative because the system loses energy. When work is done on a system, the system gains energy. For example, someone compressing a reaction vessel would do work on a system. This is positive because the system gains energy.

[Madelyn_Rios_2c]

negative work: work is done by the system
positive work: work is done on the system

[Samantha Toscano 2C]

+ work = work is done on the system
- work = work is done by the system

[Nyah Zhang 1E]

Work is negative when it is done by a system and positive when it is done on a system.

[Kimberly_martinez2I]

If work is done by the system then it will be negative . If work is done on a system then it will be positive.

[Coraly De Leon]

Hello,
Just as my peers mentioned, work will be negative when energy is being added to the system.

[Caitlyn Lo 2F]

Work is done by the system when work is negative and work is done on the system when work is positive.

[Rebekah Jung 1C]

Negative work means the system is doing work rather than having work done on it.

[Talia Tam 3L]

Negative work means the system is doing work and therefore losing energy. When work is done on the system, it gains energy and work is positive.

[Grant_2A]

Work done by the system is negative because it is leaving the system
work done on the system is positive because it is getting put into the system again.

[Sabira Mohammed 3I]

When work is done on the system, it's gaining energy, so work is positive. When work is done by the system, it's losing energy, so work is negative.

[Evonne Chau 2I]

Hi Justin,

When the value of work is negative, work was done BY the system, and the system lost energy. This means the system is expanding. When the value of work is positive, work was done ON the system by the surroundings. This means the system is being compressed.

[oliviahelou]

That means that work is done by the system, as it is losing energy (there's a negative sign).

[Jessica Sun 2I]

When work is negative, that means that energy is leaving the system as work and the system is doing the work. If work is positive, the surroundings are doing work on the system and the system is gaining energy as work.

[Ainsley DeMuth 1H]

In this class we have been looking at the system so when work is done on the system or to the system, work will be positive. However, when work is done by the system, work will be negative. This is the case because in the case of work is being done by the system for example, the system is losing the energy done by work and therefore the value is negative.

[Darren Apostol 2L]

If it's negative, energy is lost (system does the work), and if it's positive, energy is gained (something else is doing work on the system).

[Polo Morales 3C]

Negative work means that the system is losing energy to its environment. It is doing work to its surroundings. Positive work means work is being done to it by the surroundings. Hope this helps!

[Polo Morales 3C]

Negative work means that the system is losing energy to its environment. It is doing work to its surroundings. Positive work means work is being done to it by the surroundings. Hope this helps!

[Aryan Gajjar 3D]

The negative sign in the work equation is significant because it suggests that when the volume of the system grows (V is positive), the gas in the system loses energy as work. If the gas is contracting, however, V is negative, and the two negative signs combine to make the work positive, indicating that energy is being added to the system.

[Rachel Bartley 2B]

It would be the other way around. When work is negative, the system is doing work, and when it is positive, then work is being done on the system.