
So far you know that:
 Angular momentum (L mom or H o
) is a vector quantity that defines an object’s rotation about an axis of rotation (i.e. any object or fluid that rotates about an axis has angular momentum). It is a measure of the tendency of an object to spin.

L mom is demo) used to develop kinetic energy and to stabilize moving objects (bike wheel
 L mom is dependent on the object’s such that mass , radius (inertia) and angular velocity
L mom
= mr
ω
Units: English = slug.ft
2 /s
Metric/SI = kg.m
2 /s

 Angular velocity ( ω) can have units of:
A) radians per second (rad/s) – the metric/SI unit or;
B) revolutions or rotations per minute (rpm) – the English unit.
Interesting pt: The corresponding unit in the International System of Units (SI) is hertz (symbol Hz) or s -1 (1/second). Revolutions per minute is converted to hertz through division by 60.
 Often times it is necessary to convert from either rpm  rad/s OR rad/s  rpm
 To convert from rpm to rads simply x by 0.1047rad/s* ex. 65rpm= 65 x 0.1047rad/s = 6.8rad/s
 To convert from rads to rpm simply x by 9.55rpm* ex. 6.8rad/s= 6.8 x 9.55rpm = 65rpm
* Conversion factors taking from pg.7 of Engineering Toolbox

 When working with angular momentum the product of mass x radius is INERTIA(I) where I=mr
 So, the formula L=mr ω changes to L=Iω
 Thus, the angular momentum of an object is affected by an object’s inertia (mass and radius) and angular velocity.
 If shape of object changes, inertia will change (see wkbk p.43) .
 For example I=mr 2 for a wheel but I=1/2mr 2 for solid cylinder.
 So, if you are calculating the angular momentum of a wheel L=I ω changes from L=(mr) ω to L=(mr 2 ) ω
 For your spin board activity you assumed that Adam and Jake were cylinders therefore their inertia can be calculated using I=1/2mr 2 .
 Therefore, their angular momentum can be calculated using:
L= (1/2mr 2 ) ω
Note: If radius changes (ex. Radius for Arms Out vs Radius for Arms In don’t forget to also use the correct value for “r”)

Simple Angular Momentum
 Let’s calculate simple angular momentum (as you did in your activity)
 Let’s try another example:
A 900kg cylindrically shaped communications satellite is launched into orbit from the space shuttle. The satellite’s radius is 0.7m. It spins about its own axis at 30rpm.
What is the: a) moment of inertia of the satellite b) angular momentum of the spinning satellite due to its spin?
Classwork/Homework: Complete pp.55-
57 (Let’s review units a-d and Problems
1-3)
*Whatever is not completed in class must be done for homework