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p140w07_ct_08

p140w07_ct_08 - Racquetball Striking a Wall Copyright Loren...

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Physics 140: Winter 2007 Lecture #8 January 30, 2007 Dave Winn Racquetball Striking a Wall Copyright: Loren M. Winters Mt. Etna Andrew Davidhazy

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1 st exam information First exam: Thursday Febuary 1st from 6:00-7:30 PM We will start promptly Bring a calculator Bring a 3”x5” card with whatever you want to remember (both sides OK) Room Assignments Uher: Angel Hall aud C Bechetti: 1400 Chem Skalsey: 1800 Chem Cole: 1800 Chem Bobkov: 170 Denn Winn: 182 Denn
Motion in more than one dimension Second law in vector form: Velocity changes are in the direction of the force Any component of velocity perpendicular to the force is unchanged We are considering two special cases of 2D motion: Projectile motion: force always in one direction One component of motion “uniform and perpetual” One component feels a constant force Uniform circular motion Force always perpendicular to the motion: speed is unchanged dt v d m a m F r r r = = Σ

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Realistic projectile motion with air friction Barry Bonds hits a baseball at 120 mph at a 45 ° angle. If there were no air friction it would travel around 910 feet! Barry Bonds hits a baseball at 120 mph at a 45 ° angle. With air friction it instead travels only around 490 feet… v r g m r air F r Air friction is always opposite motion!
Another special 2D motion Uniform circular motion, another special case of 2D motion Object traveling at constant speed on a circle needs a force of fixed size, always to motion, to keep moving in a circle F r v r v r F r v r F r v r F r

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