The force that slows down the movements of an object through a liquid or gas is known as drag, or air resistance. In some cases, this force is also referred to as friction, but classically, friction occurs in solid objects.
The drag force will always decrease the velocity of a fluid. The standard equation for drag force is: drag force = 1/2pv 2 C D A, with C equaling the drag coefficient. Drag will always depend on the size, shape and speed of an object, as well as the fluid. The drag coefficient also depends on the Reynolds number. To calculate drag, all of this information will be needed.