In a glass of milk, the particles are in constant motion due to their kinetic energy. The milk is a colloidal suspension, meaning that it contains tiny particles of fat, protein, and other substances dispersed throughout the liquid. These particles are much smaller than the wavelength of visible light, so the milk appears opaque.

The fat particles in milk are the largest and most abundant, and they are responsible for the milk's white color. The fat particles are surrounded by a layer of protein molecules, which helps to keep them from clumping together. The protein molecules also interact with the water molecules in the milk, forming a network that gives the milk its characteristic texture.

When milk is heated, the protein molecules begin to denature, which means that they lose their shape and structure. This causes the fat particles to clump together and rise to the surface, forming a layer of cream. The milk also becomes thinner and less viscous as the protein molecules break down.

The motion of the particles in milk is also affected by temperature. When milk is cold, the particles are moving more slowly and the milk is thicker. When milk is heated, the particles move more quickly and the milk becomes thinner.

The movement of the particles in milk is also affected by agitation. When milk is shaken or stirred, the particles collide with each other more frequently and the milk becomes frothier.