Tis the season to be skiing, even though I hate winter and i do not ski myself physics is applied when you ski. When you look at skiing you can apply Newton's three laws the first law being an object in motion will stay in motion and object at rest will stay at rest until acted upon by an outside force. This is how a skier is able to go downhill without stopping, the gravity is what puts the skier in motion and the skier will not stop until an outside force acts upon it. That outside force could be another skier, a bump on the hill, or a tree that just happens to be there. Newton's second law states that force equals mass x acceleration. Using this we can calculation how much force we have or going to have when we go down a hill by taking our mass and multiplying it by our acceleration. By using this we can calculate our force we can also figure out how much it would hurt if we were to hit a tree. And our last law states that for every action there is an equal and opposite reaction. This is used when we are using our poles to push the ground away from us to get started, in a sense the ground is pushing back.