Sunday, November 16, 2008

Impulse


Why is a foam football easier to catch than a leather one? I always had an idea that the foam football was easier to catch because it was softer and easier to grasp, but I now know the physics behind this innate idea. When a football hits your hands, it exerts a force upon you. To stop the football and hold on to it, your hands must exert the exact same force back upon the football to create a net force of 0 N and reduce the ball's velocity to zero. Impulse, defined as the change in momentum of an object, equals Force times time. With this information, you know that an extension of the time of a catch will decrease the force exerted by the ball at any given second. The foam football, which compresses as you catch it, exerts a smaller force over a longer time, while the leather football does not compress as you catch it, and thereby exerts a larger force on your hands over a shorter time period. This is why a foam football is easier to catch than a leather one.

Sunday, November 2, 2008

Newton's 2nd Law of Motion


Now that tennis season is finished, I decided to write my journal about the physics involved in paddling, the sport I am doing now. In a race, the speed of the canoe is all important to winning. According to Newton's second law of motion, the acceleration of an object is equal to the net force acting on it divided by its mass. In the case of paddling, the net force on the canoe equals the sum force of everyone's paddle against the water minus air/water resistance. To increase the net force on the canoe, the paddler should be as strong as possible to exert more force on the water, but not too heavy, for as the paddler's mass increases, the boat' acceleration decreases.