# Internal energy present, is there conservation of energy?

Hmm. This is another thing i'm unsure abt.

When some mechanical energy is converted to internal energy, can we still say that energy is conserved?
Can the internal energy be negative?

Thanks for answering my qns :)

## Answers and Replies

Mapes
Homework Helper
Gold Member
When some mechanical energy is converted to internal energy, can we still say that energy is conserved?
You're going to need to be more specific. Yes, energy is always conserved.

Can the internal energy be negative?
Energy is always relative to a certain reference, so there's no problem with energy being negative.

Energy is always conserved, except when it isn't.

Energy is always conserved in the Classical Physics folder; not always conserved in others. :uhh:

HallsofIvy
Homework Helper
Energy is always conserved in a "closed system"!

Of course, a "closed system" is defined as one in which energy is conserved!

Energy is always conserved in a "closed system"!

Of course, a "closed system" is defined as one in which energy is conserved!
So that's the difference between the folders.

Or is $$\partial_\mu p^\nu [/itex] folder covariant?, [tex]\frac{d}{df}\partial_\mu p^\nu = 0$$

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