1. Diffusion

Simple diffusion is a process by which two gases or fluids mix, without any mechanical help. This happens because all molecules are in a continual state of movement - random, erratic movement. They bounce off each other as they move, and in the process they spread out - or diffuse.

If you think of the last time you noticed burnt toast, you will have an excellent example of diffusion since the smoke near the grill very quickly spreads out over the whole room.