The flow of fluids in a material, such as air, is a physical phenomenon known as convection. The flow of fluids is often characterized by single- or multi-phase compositions. It occurs as a result of body forces acting on a fluid. The most common body forces are gravity and density. This article will provide an overview of the properties of fluids and describe some common examples. The process of convection can be explained with simple diagrams.

The process of convection occurs when two parts of a fluid differ in temperature. It is an important mechanism for heat transfer in the outermost interiors of stars and black holes. This process can be invisible or visible and can take place at extremely fast speeds. In addition to being a vital component of stars, convection occurs in accretion disks of black holes. Some research suggests that these accretion disks have temperatures that can approach light speed.

The best example of convection is a thunderstorm. Warm air rises, forming saturated water drops. The smaller clouds run into bigger ones, causing the thunderstorm to form in its final stages. Even in our everyday lives, we see convection in action by steaming our beverages. As the water boils, the warmer air in the liquid moves down, replacing the hot water. The same thing occurs when we steam our coffee, tea, or other hot beverages. The heat of the fluid causes warm air to rise in a cup.