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Newton's Laws
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Newton's first law states that "an object in motion will stay in motion, and an object at rest will stay at rest unless acted upon by an outside force." This means that if there were no outside forces acting on a skier, a single stride would keep the skier moving forward indefinitely. However, there are outside forces which act on skiers. Friction is one example of an outside force. Without friction (and an object in the skier's path) a skier would not slow down after going down a hill. Newton's second law is often known as F=ma, or Force equals mass times acceleration. This explains the force a skier has when going down a hill. For example if a skier was accelerating down due to gravity and weight 100 kg, the skier's force would be 981 Newtons. This force is not too hard to imagine. Most people could guess that the heavier a person is, and the faster the person is going the greater the force would be. It is this large force that causes people to hurt themselves while skiing. Imagine crashing into another object at a high acceleration and then a lower acceleration. Obviously the force caused by the higher acceleration would be greater. Newton's third law says that "for every action there is an equal and opposite reaction." This means that the skier is excerpting a force on the ground, and the ground is excerpting an equal and opposite force on the skier. For example if a skier is excerpting the force m*g on the ground, the ground is exerting a normal force on the skier equal to -m*g. Another example of Newton's third law is if a skier is forced to ski over some small trees. When the skier bends them over, the skier is exerting the same force on the trees as they are excerpting on the skier. This might seem false because the trees are left bent, and the skier continues on unaffected. However, the skier is much more massive than the twigs, and therefore the effect on the trees is greater. |
