week6-1

# week6-1 - Momentum and Impulse How can we describe the...

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Momentum and Impulse How can we describe the change in velocities of colliding football players, or balls colliding with bats? How does a strong force applied for a very short time affect the motion? Can we apply Newton’s Laws to collisions? What exactly is momentum ? How is it different from force or energy? What does “ Conservation of Momentum ” mean?

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What happens when a ball bounces? When it reaches the floor, its velocity quickly changes direction. There must be a strong force exerted on the ball by the floor during the short time they are in contact. This force provides the upward acceleration necessary to change the direction of the ball’s velocity.
What happens when a ball bounces? Forces like this are difficult to analyze: Strong forces that act for a very short time. Forces that may change rapidly during the collision. It will help to write Newton’s second law in terms of the total change in velocity over time, instead of acceleration: F net m a m v t

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Momentum and Impulse Multiply both sides of Newton’s second law by the time interval over which the force acts: The left side of the equation is impulse , the (average) force acting on an object multiplied by the time interval over which the force acts. How a force changes the motion of an object depends on both the size of the force and how long the force acts. The right side of the equation is the change in the momentum of the object. The momentum of the object is the mass of the object times its velocity. F net m a m v t F net t m v p m v
Momentum and Impulse A bowling ball and a tennis ball can have the same momentum, if the tennis ball with its smaller mass has a much larger velocity.

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week6-1 - Momentum and Impulse How can we describe the...

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