Angular Momentum

Friday, November 7

A B C D F0

1

2

3

4

5

6

7

8

Exam 3 Average = 83

Today: Angular Momentum

Chapter 9 Section 7

Angular Momentum, L

L I

Compare to linear momentum

p mv

Direction??

Conservation of Angular Momentum

i f

i i f f

L L

I I

What is needed for L to be conserved?

Problem 9.34Divers change their body position in midair while rotation about their c of m. A diver leaves the board with her body nearly straight, then tucks into a somersault position. If her moment of inertia in the straight position is 14 kg•m2 and in tuck is 4.0 kg•m2 by what factor is her angular velocity when tucked greater than when straight?

Problem 9.34

14.3.5

4.0

i i f f

f i

i f

I I

I

I

This week’s Laboratory Experiment

0.471kg 1.343kg

248degrees/s 64 degrees/s

initial final

initial final

M M

L conserved?

2.039

2.026

% 0.6

initial initial

final final

M

M

difference

Problem 9.32

What is the angular momentum of a bar rotating at 120 rpm. The bar rotates about its center, has a mass of 500g and is 2 m long.

Problem 9.32

2 2

2

10.1667 kg m

12(120rpm/60s/min)*2 rad/rev 4 rad/s

2.1 kg m / sec

I ML

L I

MondayEnergy and Work

Reading: 10: 1-3Problems: 9: 30, 32, 34, 35

A closed (isolated) system has a total energy E which is constant, but the form of the energy can change. For example, thermal, kinetic, chemical, …We shall be concerned with the conversion of one kind of energy into another and the exchange of energy with the outside world.