PHY183-Lecture23 - February 24, 2006 Physics for...

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Unformatted text preview: February 24, 2006 Physics for Scientists&Engineers 1 1 Physics for Scientists & Physics for Scientists & Engineers 1 Engineers 1 Spring Semester 2006 Lecture 23 February 24, 2006 Physics for Scientists&Engineers 1 2 Momentum Review Momentum Review Linear Momentum Newtons 2 nd Law Impulse Average Force r p = m r v r F = d r p dt r J ! r Fdt t i t f " r J = ! r p r J = r F av ! February 24, 2006 Physics for Scientists&Engineers 1 2 Momentum Review Momentum Review Linear Momentum Newtons 2 nd Law Impulse Average Force r p = m r v r F = d r p dt r J ! r Fdt t i t f " r J = ! r p r J = r F av ! t February 24, 2006 Physics for Scientists&Engineers 1 3 Impulse and Car Safety Devices Impulse and Car Safety Devices Car collision: very large impulse (cannot be changed) Typical collision time is very short Since , this means a very large force acting on the driver All passive safety devices (seat belt, air bag, crash crumple zones) are designed to extend time interval and thus to reduce average force r F av = r J ! t February 24, 2006 Physics for Scientists&Engineers 1 4 Impulse and Sports Impulse and Sports Why can one hit for more power with less tension on the tennis racket strings? Answer: relationship between impulse, force, and time If average force is fixed, increasing the contact time between racket and ball increases impulse given to ball r J = r F av ! t February 24, 2006 Physics for Scientists&Engineers 1 5 Quiz 22.1 Quiz 22.1 Jack swings at a 0.2 kg ball that is moving west with a velocity of 40 m/s and hits a line drive. The ball leaves his bat with a velocity of 40 m/s due east. Assuming the ball is in contact with the bat for 0.010 s, what is the average force of the bat on the ball? a) 800 N East b) 1600 N East c) 1600 N West d) 800 N West February 24, 2006 Physics for Scientists&Engineers 1 6 Quiz 22.1 Quiz 22.1 Jack swings at a 0.2 kg ball that is moving west with a velocity of 40 m/s and hits a line drive. The ball leaves his bat with a velocity of 40 m/s due east. Assuming the ball is in contact with the bat for 0.010 s, what is the average force of the bat on the ball? a) 800 N East b) 1600 N East c) 1600 N West d) 800 N West 0.2 (40 ( 40) / ) 16 kg m/s east 16 1600 N east .01 p kg m s p F t ! = " " = ! = = = ! February 24, 2006 Physics for Scientists&Engineers 1 7 Collisions Collisions Collisions of two (or more) objects, or one object with a wall Two cars in a traffic accidents Two billiard balls One billiard ball bouncing off the wall Asteroid hitting Earth Two air molecules bouncing off each other Question : If we know the momenta of the two objects before the collision, can we predict the momenta after the collision? February 24, 2006...
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This note was uploaded on 03/19/2008 for the course PHY 183 taught by Professor Wolf during the Spring '08 term at Michigan State University.

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PHY183-Lecture23 - February 24, 2006 Physics for...

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