1. Describing Rotational Motion
Chapter 8

2. Linear to Rotational (Angular)
Angular displacement: distance traveled around a circle or arc (measured in radians or rad)
Angular velocity: change in angular displacement over time (measured in rad/s)
Angular acceleration: change in angular velocity over time (measured in rad/s2)

3. Linear to Angular (Rotational)
We can use the same basic principles as before.
The only difference will be the motion will be in a circle rather than a straight line.

4. Torque A force that causes an object to rotate
Measures how effective a force is in rotating an object
Measured in Newton meters, Nm (in America, known at foot pounds, ft lb)

5. Time for Rotation Answer the following:
Materials
Calculator
Objective
Determine the angular displacement and velocity of the hands on a clock.
Answer the following:
How far does the second hand move every 10 s?
What is the angular velocity for each hand (second, minute, hour) in rad/s?
Find angular displacement in rad for each hand in 20 min?
There is a speck of dust on the second hand. Where on the hand would it move the fastest? The slowest?

6. t = F r sin q Torque (Equation #1)
Also known as force at a distance from the equation:
t = F r sin q
t is torque (Nm)
F is force (N)
r is lever arm length or radius (m)
q is the angle between F and r (degrees)

7. Torque (Equation #2) F = m a  t = I a
Using the same argument as we did with angular equations of motion, we can find an angular equation for force.
F  t (torque, Nm)
m  I (moment of inertia, kgm2)
a  a (angular acceleration, rad/s2)
F = m a  t = I a

8. Moment of Inertia p206 Known as rotational mass
Based on shape and pivot point
In general, a spinning point-sized object will have a moment of inertia of m r2
Units: kg m2
p206

9. Torque Lab Objective: Use knowledge of torque to balance. Materials:
Meter stick
Binder clips
Masses
Hangers
Ring stand (clamp)
Procedures:
Set-up equipment like demo
Determine the mass of the hanger holder using materials given (___ g)
Place hanger with 20 g at 70 cm
Calculate and record where 50 g (silver hanger) should be place on the other side for balance (_____ cm)
Place silver hanger at calculated position
Determine how close your results were (off by ___ cm)

10. Ch8 Homework 72. 0.6 rad 75. 197 rad/s, 492 rad 82. 3.8 Nm
N right, 37 N left
rad/s, 16 rev,100 rad