1. Week 7: Circular Motion
Newtonian Thinking About Circular Motion
Centripetal force
Dynamics equations for circular motion
Kinematics equations for circular motion
Units: angular distance, velocity, acceleration
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2. Ponderable #1
Assign roles in your group and discuss the problems
for today that were posted on Blackboard. You may
check your work against the solutions that now are
available on Blackboard.
Where you are having difficulty understanding the
solutions, discuss them with the other groups at your
table.
Where helpful, remember to draw a picture of the
problem first and then create the Free Body Diagram.
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3. Some Circular Motion Terms and Concepts
Recall that 1 revolution = 360° = 2π radians
» Frequency is in revolutions/second
» Period is in seconds/revolution
f = 1/ P
• If you swing a ball in a circle, the speed is constant but
the velocity is not constant, since the direction is
changing.
• must be some acceleration: centripetal acceleration!
• … toward the center of circle
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4. Describing Rotation
What can we ask about a rotating object?
How much did it rotate? Angular displacement ∆θ
How fast did it spin? Angular velocity ω
Why are these useful? Every point on a rotating object
has the same angular velocity!
linear angular
displacement ∆x ∆θ rad
velocity v = ∆x/∆t ω = ∆θ/∆t rad/sec
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7. Ponderable #2
In your groups, work on the following problem:
A CD drive in a computer spins the 12-cm-diameter
disks at 10,000 rpm.
a.What are the disk’s period (s) and frequency (rev/s)?
b.What would be the speed of a speck of dust on the
outside edge of this disk?
c.What is the acceleration that this speck of dust
experiences?
Discuss your results with other students at your table.
Include your work in your group’s activity report.
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8. Ponderable #3
In your groups, work on the following problem:
A hamster runs in its wheel for 4.3 hours every
night. If the wheel has a 6.8 cm radius and its
average angular velocity is 3.0 radians per second,
how far does the hamster run in one night?
Discuss your results with other students at your table.
Include your work in your group’s activity report.
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9. Tangible #1
Find a way to measure the angular and linear speeds and
accelerations of a mass at the end of a string when you twirl
the mass around in a circle.
Make the measurements for 3 different lengths of the string.
Discuss your results with other students at your table.
Include your work in your group’s activity report.
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10. Tangible #2
In your groups, use ACCESS to work the following:
Wheel A of radius rA is coupled
by belt B to wheel C of radius
rC = 25 cm. The angular speed
of wheel A is increased from
rest at a constant rate of 1.6
rad/s2. Find the time for wheel
C to reach a rotational speed
of 100 rev/min, assuming the
belt does not slip.
Discuss your results with other students at your table.
Include your work in your group’s activity report.

11. Summary of Today’s Learning
1. Discuss your review sheets at your table.
2. Answer WADYLT* (if assigned today).
3. Prepare and submit your group activity report.
*What, if Anything, Did You Learn Today? 11