JoinScience 101: What causes convection?
Convection is when different parts of a fluid move in a more-or-less circular path, with parts of the fluid at the bottom moving to the top and vice versa. Here fluids refer to both liquids and gases. Convection happens when you have two fluids together that are different densities, but we can come up with a more detailed explanation than that. In doing so, we’ll concentrate on liquids because they’re easier to mess around with.