A force that opposes the motion of a body. It acts on the body in a direction opposite to the direction of the velocity of the body. For example, a ball-bearing falling in a cylindrical glass jar containing oil experiences the downward pull of gravity and a resistive force upwards caused by the oil acting to oppose the motion of the falling ball-bearing. Other examples are friction and aerodynamic drag. When there is a resistive force, the principle of conservation of energy does not hold, but the work–energy principle does hold.