Notes: Monday, February 25, 2013 Title: Momentum and Impulse EQ: Why do gymnasts use floor mats that are very thick? Momentum • Momentum = mass × velocity • The letter we use to say momentum is p • So another way of writing the equation p=mv • A moving object can have a large momentum if it has a large mass, high speed, or both. Applied Question • When would a roller skate and a truck have the same momentum? Impulse • An impulse is a change in momentum and depends on the force applied and the length of time it acts. • Or impulse = force × time • Impulse = change in momentum Ft=∆mv » Remember ∆ means change in Changes in Momentum Increasing Momentum • To increase momentum the most you want to apply the greatest possible force for the longest possible time • Baseball players do this by swinging as hard as possible and by following through. Decreasing Momentum • To decrease momentum without causing damage the best way is use less force over an extended amount of time. • When padding is used collisions happen over longer time, such that the change in momentum cause less damage. Applied Question • When a dish falls, will the impulse be less if it lands on a carpet than if it lands on a hard floor? Bouncing • The impulse required to bring an object to a stop and then throw it back again is greater than the impulse required merely to bring the object to a stop. Happy Sad Physics Spheres Concept Checking Questions • A lunar vehicle is tested on Earth at a speed of 10 [km/h]. When it travels as fast on the moon, is its momentum more, less, or the same? • When you ride a bicycle at full speed and the bike stops suddenly, why do you have to push hard on the handlebars to keep from flying forward. Concept Checking Questions • What does an airbag do to help you reduce damage to your head in a car accident? • When jumping from a significant height, why is it advantageous to land with your knees slightly bent?