About the equation for net work done by nonconservative forces

[FisherDude]

Wnc = delta (kinetic energy) + delta(potential energy)

(Work done by nonconservative forces) = (change in kinetic energy) + (change in potential energy)


Now, my professor gave us this formula instead of the one above: W - H = (change in kinetic energy) + (change in potential energy), where H = heat loss, W = work done.


What I'm confused about is whether heat loss still counts as work...since the heat loss is caused by a frictional force such as air resistance, and the air friction would act opposite the direction of motion, so it seems that the air friction does negative work. so H still counts as work?

Btw, for the first equation, its not assuming that there's no heat loss, right? (due to friction) So if its not assuming that there's no heat loss, then that would also include work done by friction (which would equal H in the second equation)? (negative work)


Any help at all would be greatly appreciated..

 

[Nabeshin]

The first equation is completely correct. Any energy lost due to friction and heat will be manifested in a change in total energy (KE+PE), it's just not explicitly stated in the equation like in your other one. Heat loss does count as work, seeing as it is caused by a force (friction, or air resistance) applied through a distance. Indeed it is negative work, which means it takes energy out of the system.

 

[Moetasim]

Hello there!

Firstly, let's clarify the difference between work and heat. Work is the transfer of energy from one object to another due to a force acting over a distance. Heat, on the other hand, is the transfer of energy due to a temperature difference between two objects.

In the first equation, Wnc = ΔKE + ΔPE, we are considering the work done by nonconservative forces, which includes both work done by external forces and work done by friction. Friction is a nonconservative force because it dissipates energy and does not conserve it. So, when we say ΔKE + ΔPE, it includes the work done by friction as well.

In the second equation, W - H = ΔKE + ΔPE, we are considering the work done by all forces, including both conservative and nonconservative forces. Here, H represents the heat loss due to friction, which is a nonconservative force. So, in this equation, we are taking into account the work done by all forces, including the work done by friction (represented by H).

To answer your question, yes, heat loss (represented by H) still counts as work in this equation, but it is important to note that it is negative work. This is because heat loss is caused by a frictional force, which acts opposite to the direction of motion. So, in the equation, it is represented as a negative value.

In conclusion, both equations are taking into account the work done by friction, but the second equation also includes the heat loss (represented by H) as a form of negative work. I hope this helps to clarify your confusion. Keep up the good work in your studies!