Short Notes:

Skiers can race downhill - often at more than 160 km per hour - because they are able to overcome friction, the force that prevents sliding between two objects. When a skier first steps onto a slope, friction causes the skis to stick to the snow. But the skier's weight exerts a force perpendicular to the slope that melts a thin layer of snow under the skis, creating a film of water. This film acts as a lubricant, greatly reducing the braking force of friction and allowing the force of gravity to pull the skier down the slope. As the skier moves forward, heat generated by the skis sliding against the snow continuously melts new snow underneath the skis, maintaining the watery film. A skier can gain even more speed by coating the bottoms of the skis with wax, which repels water and further reduces friction.

For the same reason, ice-skaters glide over a thin film of water, rather than on the ice itself. The great pressure that is exerted by the skates' narrow blades causes the ice to melt, nearly eliminating friction.

Click here for a Flash presentation on skiier in motion.