Internal Energy

Sum of all the microscopic forms of E.  
Sum of all Kinetic and Potential Energies of the molecules of a system.
U (or E)
Hyper Physics link

Does not include translation or rotation of body as a whole.
Cannot measure total.  Can only measure

First Law Statements:

- A thermodynamic system can store or hold energy.  This Internal Energy is conserved.

- The internal energy of the universe is constant.

- The change in the internal energy of the universe is zero.

ΔUuniverse = 0

- The sum of energy changes in the system and surroundings is zero.

ΔUuniverse = ΔUsystem + ΔUsurroundings = 0

- For an isolated system:        ΔUsystem = 0

- For a closed system:        ΔUsystem = q + w

- For a closed system at constant volume with only PV work:

ΔUsystem = qv