The motion of a skier is determined by the physical principles of the conservation of energy and the frictional forces acting on the body. For example, in downhill skiing, as the skier is accelerated down the hill by the force of gravity, his gravitational potential energy is converted to kinetic energy, the energy of motion. In the ideal case, all of the potential energy would be converted into kinetic energy; in reality, some of the energy is lost to heat due to friction. One type of friction acting on the skier is the kinetic friction between the skis and snow. The force of friction acts in the direction opposite to the direction of motion, resulting in a lower velocity and hence less kinetic energy. The kinetic friction can be reduced by applying wax to the bottom of the skis which reduces the coefficient of friction. Skiing is a fun and easy example of how physics work in our lives.