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:
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