This preview shows pages 1–9. Sign up to view the full content.
Rotation
Physics 7B  Lecture 7
Prof. John Conway
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document Bicycles  PRS
•
If you are on a bicycle standing still, you will fall over very
quickly.
If the bike is moving you do not fall over as easily,
because
a. it’s easier to turn against the fall when moving.
b. the rotating wheels generate a torque that keeps the bike
from falling.
c. the force of gravity on rotating objects is reduced.
d. it takes more torque to cause the bike to fall over when
the wheels are rotating.
e. the rotating wheels tend to be vertical due to their
angular momentum.
New Terms We’ll Master
•
angular velocity
→
how fast something rotates
•
rotational inertia (a.k.a. moment of inertia)
→
“rotational” mass
•
angular momentum
→
quantity of rotational motion
•
torque
→
angular force
Each of these concepts has a
direct analog with linear motion
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document Angular
㲗
Linear
quantity
linear
angular
position
x
θ
velocity
v
ω
mass
m
I
momentum
p = mv
L = I
ω
force
F
τ
energy
1/2 mv
2
1/2 I
ω
2
impulse
F
Δ
t
τ
Δ
t
Angular Velocity
•
ω
is the Greek letter omega
(NOT w !)
•
ω
is called the angular velocity
•
units of angular velocity: radians per
second, or simply s
1
(same as frequency!!)
1 revolution = 2
π
radians
rev/sec =
ω
/2
π
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document Circular motion
‣
Two masses connected by rod: dumbbell
‣
No net displacement!
‣
Position, velocity, momentum vectors are moving
Circular Motion Vectors
r

a

v

v =
ω
r
a =
ω
2
r
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document Angular Velocity
•
Angular velocity for constant rotation:
θ
(t)=
ω
t
ω
=d
θ
/dt
Our dumbbell has no
linear momentum, but
it does have
angular momentum
This is the end of the preview. Sign up
to
access the rest of the document.
This note was uploaded on 03/30/2010 for the course PHY 7 taught by Professor Staff during the Spring '08 term at UC Davis.
 Spring '08
 Staff
 Physics

Click to edit the document details