We need to hire note takers (one each for PH 212 and PH 222).
The pay for providing such notes is usually $50 to $100 per course.
If you have at least a 2.5 GPA and take accurate, legible notes, and you'd like to apply, then either….
Go online to sign up, at: http://ds.oregonstate.edu/notetaker
Or visit the DAS office in A200 Kerr Admin. Bldg.
Note: Selection and hiring is done on a first-come/first served basis.
1/8/16 Oregon State University PH 212, Class 3 1

Motion and preferred (SI) units for a rotating (rigid-body) object
Entire rotating object A point on the object at radius r (m) from center
Angular measure Translational measure ang. position: q (rad) arc position: s = q r ang. displacement: Dq (rad) arc displacement: D s = ( Dq ) r
(m)
(m) ang. velocity: w (rad/s) velocity: v = w
X r = ( r w )
T ang. acceleration: a (rad/s 2 ) tangential accel.: a
T
= a
X r = ( r a )
T
(m/s)
(m/s 2 ) radial accel: a
R
= w
X v = ( r w 2 )
R
= ( v 2 / r )
R
(m/s 2 )
(m/s 2 ) total acceleration: a = a
T
+ a
R
(m/s 2 )
1/8/16 Oregon State University PH 212, Class 3 2

What’s the magnitude of the total acceleration, a , of a ladybug riding on the rim of a disk (radius = 30.0 cm) that’s rotating at a constant 60.0 rpm?
1.
2.
| a | = 0 m/s 2
| a | = 1.89 m/s 2
3.
4.
| a | = 7.00 m/s 2
| a | = 11.8 m/s 2
5.
Not enough information.
(What would you need to know to be able to state the direction of the a vector?)
1/8/16 Oregon State University PH 212, Class 3 3

In uniform circular motion:
1/8/16 Oregon State University PH 212, Class 3 4

Modify the previous problem: What is the total acceleration, a total
(both magnitude and direction), of a ladybug riding on the rim of a disk (radius = 30.0 cm) that is rotating at (+)60.0 rpm and is accelerating at –17.5 rad/s 2 ? At the moment in question, assume that the ladybug is at a position q = p /2.
1/8/16 Oregon State University PH 212, Class 3 5

Newton’s Second Law in r-, t-, zcomponents:
1/8/16 Oregon State University PH 212, Class 3 6

Newton’s Laws Still Apply:
Free-body diagrams practice for objects in circular motion
S F = m a is still true, even when a is a sum of a
T and a
R
.
Consider how to graph and solve these examples…
• A kid sitting on the floor of a merry-go-round
• A ball swinging around a pole
• A ball swung about vertically in a circle on a string
• A car going around a curve
• A car cresting the top of a hill
1/8/16 Oregon State University PH 212, Class 3 7