The principles of energy and momentum can also apply to rotations inside atoms. For example the following types of rotations:

## Orbital rotation of electron

The orbital rotation of electron around the nucleus. This contributes to total angular momentum of object at the large scale.

## Spin of Particles

The spin of particles also contributes to total angular momentum of object at the large scale. Spin is quantised to 1/2 integer for fermions and integer multiple for bosons.

Even particles which take up no space have spin.

According to quantum theory we cant know the actual spin, just the probability function.

Unlike rotations at the scale that we experience, a complete rotation is 720 degrees not 360 degrees so we must use SU(2) such as quaternions to calculate rather than R(3) such as matricies.

## Isospin

Isospin does not contribute to the total angular momentum of object at the large scale.

Isospin determines if a particle is a proton or a neutron.