Brownian motion
Temperature is movement of atoms and molecules.
This movement of for example the molecules in liquid, causes constant collisions with other molecules. Due to these frequent collisions is the movement of the liquid molecules completely at random and no orderly structure exists. How intensive, respectively fast, this trembling motion on a molecular level really is, depends on the temperature and viscosity of the liquid. Here high temperatures mean a faster motion.
If the liquid contains a particle, so it also constantly collides with liquid molecules, causing a trembling motion of the particles. The speed of this trembling motion of the particle though depends besides on the viscosity and temperature of the surrounding liquid also on the particle size. The density, respectively the mass of the particle is not figured in though.
