Transcript Circular Motion

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
st
1
Law
 Newton’s 2nd Law

Force needed to cause an
acceleration
A new force…
force – force that
causes an object to follow a
circular path
 Centripetal
What’s wrong with this picture?
Be careful…

Centripetal force sometimes called
“centrifugal” force

A “fictitious” force
Centripetal Acceleration
 ac
= v2/r
Circular Motion Problems

#1 a - d
Back to Isaac...
F = ma
Fc = m (v2/r)
Fc = mv2
r
Circular Motion Practice


#1 e
#2
Centripetal Force Lab
Fill in the blank…

force
A ____________
causes acceleration.

torque
A ____________
causes rotation.
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!