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

## Presentation on theme: "Circular Motion. Which horse on a merry-go-round moves faster… One on the outside rail One near the inside rail?"— Presentation transcript:

Circular Motion

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

Or…how about a turntable?

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

Interesting application… Rims of train wheels are tapered

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

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

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

What’s wrong with this picture?

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

Centripetal Acceleration a c = v 2 /r

Circular Motion Problems #1 a - d

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

Circular Motion Practice #1 e #2

Centripetal Force Lab

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

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

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

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

Circular Motion Practice #3

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

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

Why do giraffes have a slower gait than Chihuahuas?

Why do longer pendulums swing more slowly than shorter ones?

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

Quiz Next Class!

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