Internal Energy

There are several forms of energy that can be described as internal energy in a system.

• Translation Motion - Kinetic energy that is common in classical mechanics 1/2mv² (m = Mass v = Velocity)

Rotational Motion – Another form of Kinetic energy in classical mechanics 1/2Iw² (I = Moment of Inertia, w = Angular velocity)

Vibration Motion – Bonds inside a molecule act like small springs with a potential energy of 1/2kx² (k = Spring Constant , x = Displacement)

Intramolecular Potential Energy - Atoms tend to be ionized (have a distinct charge associated with them) this can cause a magnetic potential energy between atoms in a molecule.

Intermolecular Potential Energy – Molecules themselves can be polar, a good example of this is water with a negatively charged oxygen and two slightly positively charged hydrogen atoms. The net charge on a water molecule in zero but the molecule itself is polar having a negative and a positive end. Thus polar molecules can have a certain magnetic potential energy associated with them.

U is the commonly used symbol for internal energy.