How Are Energy and Work Interconnected in Thermodynamics?

[hwall95]

Okay i know that energy is the ability or capacity to do work. But how do you define work, as like the isn't work just the transference of energy in one form to another? Which is kinda circular reasoning. Like the rely on each other for a defintion. Is that right?

 

[Dale]

The appropriate definition of work depends on what theory you are using.

One is the mechanical definition: "work is f.d". This definition is used in basic Newtonian mechanics. In it forces are the primary things and everything else is defined based on forces. Then energy is non-circularly defined as the capacity to do work.

The other is the thermodynamic definition: "work is a transfer of energy other than through heat". This definition is used in Lagrangian and Hamiltonian mechanics as well as all field theories. In these, the Lagrangian is the primary thing and everything else is defined based on the Lagrangian. Then energy is non-circularly defined as the conserved quantity associated with time invariance of the Lagrangian.

 

[ZapperZ]

Okay i know that energy is the ability or capacity to do work. But how do you define work, as like the isn't work just the transference of energy in one form to another? Which is kinda circular reasoning. Like the rely on each other for a defintion. Is that right?

You may want to bookmark the Hyperphysics website and use it as a starting point for future querries.

http://hyperphysics.phy-astr.gsu.edu/hbase/wcon.html

Zz.

 

[hwall95]

The appropriate definition of work depends on what theory you are using.

One is the mechanical definition: "work is f.d". This definition is used in basic Newtonian mechanics. In it forces are the primary things and everything else is defined based on forces. Then energy is non-circularly defined as the capacity to do work.

The other is the thermodynamic definition: "work is a transfer of energy other than through heat". This definition is used in Lagrangian and Hamiltonian mechanics as well as all field theories. In these, the Lagrangian is the primary thing and everything else is defined based on the Lagrangian. Then energy is non-circularly defined as the conserved quantity associated with time invariance of the Lagrangian.

hahah yeah thanks i was meaning the thermodynamics definition sorry, okay thanks but when you say "other then heat energy", is that because thermal energy itself is just kinetic energy?

 

[Dale]

hahah yeah thanks i was meaning the thermodynamics definition sorry, okay thanks but when you say "other then heat energy", is that because thermal energy itself is just kinetic energy?

No, that is just the definition of work in thermodynamics. Energy can be transferred between systems either through heat, or through anything else. Anything else is called work.

The basic distinction is that heat is a rather disorganized microscopic transfer that you cannot see in detail, as opposed to things like macroscopic fields and forces.

 

[hwall95]

No, that is just the definition of work in thermodynamics. Energy can be transferred between systems either through heat, or through anything else. Anything else is called work.

The basic distinction is that heat is a rather disorganized microscopic transfer that you cannot see in detail, as opposed to things like macroscopic fields and forces.

ohhh okay thanks i understand that now, thanks heaps :)