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Gravity
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Gravity is force which acts on every massive object on earth. Therefore, it only makes sense that it plays into crosscountry skiing as well. Gravity acts on every object on earth with the force equal to mass times gravity. The force of gravity acts on the center of mass. In order to apply this concept to skiing, image that the picture below is not actually a right triangle and block. Instead pretend the block is a skier and the triangle is actually a nice little hill. 
The picture above illustrates that the force
of gravity is acting in the downward direction on the skier, with a force
of the skier's mass times the acceleration of gravity. The acceleration
of gravity is about 9.81 m/s2. However, from the illustration
above it is clear that the block-skier is skiing uphill at the angle theta.
In order to calculate the force acting on the skier in the directions parallel and perpendicular to the hill, the mg must be separated into two parts. By separating mg into parts, it becomes clear that the force of gravity pulling a skier down the hill is m*g*sin(theta). Skiers must consider the force of gravity when choosing equipment. This is because a person's weight and therefore downward pull affects equipment setup. A heavier person might need stiffer skis, whereas a light person may prefer more flexible ones. Gravity is extremely important in cross country skiing. Without it, going uphill would not be the same. Some people might think skiing uphill would be easier without a force pulling you down the hill. However, gravity also is responsible for keeping you "stuck" to the hill to begin with. Without gravity a skier would be free to float around, and that would probably be the end of skiing right there. |