Peoples Physics Concepts

9.8. Angular Momentum http://www.ck12.org

9.8 Angular Momentum

• Describe the conservation of angular momentum and apply it in both conceptual questions and in problem
  solving situations.

Students will learn about the conservation of angular momentum. How to apply it in both conceptual questions and

in problem solving situations.

Key Equations

L=Iω
~L=~r×~p=r⊥p=r p⊥
Theangular momentumof a spinning object can be found in two equivalent ways. Just like linear momentum, one
way, shown in the first equation, is to multiply the moment of inertia, the rotational analog of mass, with the angular
velocity. The other way is simply multiplying the linear momentum by the radius, as shown in the second equation.

τ=∆∆Lt

Just the same as linear momentum, the torque required to change the momentum L in t time (L/t) can be compared

to the force required to change the momentum p in t time. (p/t) Torques produce a change in angular momentum

with time.

Guidance

The same principles that hold with linear momentum conservation can be applied here with angular momentum

conservation. The direction ofLis given by the right hand rule. Simply wrap your fingers around and in the

direction the object is spinning and your thumb tells you the direction the vector is pointing.

• Angular momentum can not change unless an outside torque is applied to the object.


• Recall that momentum is a vector quantity, thus the direction a spinning object is pointing can not change
  without an applied torque.