Difference between heat and work

[Jackk]

I began to wonder how would I explain the difference between work and heat. I'd say that heat can't be fully converted into work but work can be fully converted into heat. But this is a rather general statement, imho. I was looking for some additional information and googled some stuff but no answers satisfied me. How would you state this?

 

[Drakkith]

Work: mechanical work is the amount of energy transferred by a force acting through a distance. (From wikipedia on Work)

Now heat: heat is energy transferred from one body or thermodynamic system to another due to thermal contact when the systems are at different temperatures. It is also often described as the process of transfer of energy between physical entities. In this description, it is an energy transfer to the body in any other way than due to work performed on the body. (From wikipedia on Heat)

Now energy: A system can transfer energy by means of three ways, namely: physical or thermodynamical work, heat transfer, or mass transfer.

I would say that work is energy transferred that accomplishes something, while heat is thermal energy that has the potential to be transferred or used. Thats just my personal view on it.

 

[berkeman]

I began to wonder how would I explain the difference between work and heat. I'd say that heat can't be fully converted into work but work can be fully converted into heat. But this is a rather general statement, imho. I was looking for some additional information and googled some stuff but no answers satisfied me. How would you state this?

There's a very nice PF Library entry by Hootenany about Heat:

https://www.physicsforums.com/library.php?do=view_item&itemid=121

There is also a Library entry on Work Done that may be of help.

 

[rock.freak667]

I began to wonder how would I explain the difference between work and heat. I'd say that heat can't be fully converted into work but work can be fully converted into heat. But this is a rather general statement, imho. I was looking for some additional information and googled some stuff but no answers satisfied me. How would you state this?

Usually work causes something to move, for example, a turbine to spin or a current to flow. Heat on the other hand, I think of as sort of a something like a potential energy but only some of it can be converted to work.

Like you said, all work done can be converted back into heat, but not all heat can be converted into work (by the Kelvin-Planck statement), which essentially means that work is a better quality of energy than heat is.

 

[kiwakwok]

Both work and heat described the energy transfer.
Yet, work usually refers to mechanical processes, e.g. pulling blocks, pushing piston, etc.
Whereas heat usually refers to thermal process, i.e. heat transfer due to temperature difference

 

[Sopandev]

Hello.

According to me, and a little bit of searching on the topic, Work in physics generally refers to Mechanical Work, which can be defined as the energy transferred by a force to the system, when the force moves the system through a distance.

A generalization of this Mechanical work is the Work in Thermodynamics.
The Work done in thermodynamics, can be called as the work done on the system, that changes the external mechanical make-up of the system. For example, work is done on the system when heat is provided externally and a gas expands and pushes the walls of the container outwards. Here, in a way, the expansion of the gas changes the mechanical make-up of the system by expanding it. Thus, in Thermodynamic work, heat can be regarded as the force, and the change in the physical structure of the system can be considered to be the distance through which the system moves. And the work done is the energy transferred into the system to accomplish the final state.

Heat, IMO, is the energy transferred to or from the system when another system with a different temperature is brought in some form of association, which can be contact (as in the case of conduction). Now since Work was the energy transferred in changing the mechanical make-up of the system, Heat might be the energy transfer that takes place at the molecular level, i.e. transfer of energy to the molecules due to which their energy increases.

Since increase in energy of the molecules helps in changing the external make-up of the system as well, heat energy transferred to the system is also the basic reason why the entity of work exists, or as i earlier quoted, heat can be regarded as the force.

 

[Mapes]

Another distinction is that (reversible) work carries no entropy, while heat necessarily carries entropy. This is a more general definition of work, since work includes not just mechanical transfer of energy but also transfer via electricity, magnetism, etc.

From this it follows that heat cannot be entirely transferred into work, since that would imply a reduction in entropy. Even a perfectly efficient heat engine must dump the entropy somewhere by transferring energy to a cold reservoir, and it's this energy that is unavailable to do work.

 

[sentinel]

cant you say you can consume heat and have not worked but if you have worked you have consumed heat?? HA?
heat is just there like a worker ; he can be there idle(NO work); or work and slowly die(Be consumed for work)?