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Published byKatelyn Hillyer Modified about 1 year ago

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Circular Motion

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Which horse on a merry-go-round moves faster… One on the outside rail One near the inside rail?

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Or…how about a turntable?

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More than one kind of speed… Linear speed (velocity) Distance time Greater for outside horse AKA tangential speed Rotational speed (velocity) # of rotations per unit of time Same for all horses AKA angular speed

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Interesting application… Rims of train wheels are tapered

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Washer on a string… The washer’s speed does not change, but its velocity does Centripetal acceleration

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What would Isaac say? Newton’s 1 st Law Newton’s 2 nd Law Force needed to cause an acceleration

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A new force… Centripetal force – force that causes an object to follow a circular path

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What’s wrong with this picture?

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Be careful… Centripetal force sometimes called “centrifugal” force A “fictitious” force

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Centripetal Acceleration a c = v 2 /r

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Circular Motion Problems #1 a - d

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Back to Isaac... F = ma F c = m (v 2 /r) F c = mv 2 r

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Circular Motion Practice #1 e #2

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Centripetal Force Lab

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Fill in the blank… A ____________ causes acceleration. A ____________ causes rotation. force torque

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Let’s pretend... You need to loosen a stuck bolt with a wrench... You aren’t strong enough...what do you do?

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When opening a door... Is it easier to open if you push close to or far away from the hinges?

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Torque Produces rotation = Fr Long arm, less force More force, shorter arm Ex. wrench, screwdriver, doorknob

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Circular Motion Practice #3

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Rotational Inertia Resistance to change in rotational motion Greater distance from center of mass to rotation point = greater inertia

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Why do baseball players “choke up” on the bat? “ Choking up” on a baseball bat will increase speed of swing

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Why do giraffes have a slower gait than Chihuahuas?

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Why do longer pendulums swing more slowly than shorter ones?

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Angular Momentum mvr Ice skater pulls in arms – r decreases Momentum is conserved mvr = mvr

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Quiz Next Class!

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