Major purpose of this lecture is to present Fluids. A fluid is a liquid or a gas. Fluid particles move around randomly, hitting other particles. This means that we cannot predict where one particle of a fluid will be in the future. The fluid, however, which is made of many particles, doesn’t move randomly, and we can predict where it will move. Here also briefly focus on Concentration and Diffusion. Diffusion is the spreading out of fluid particles in their container until their concentration is the same everywhere.