Angular Momentum and Inertia in Rotating Systems, Slides of Classical Mechanics

The concepts of angular momentum and inertia in rotating systems. It covers the definition of moments, shifted moments, and the law of angular inertia. The document also introduces the concept of a rigid body and angular velocity. Additionally, it discusses the definition of angular momentum in terms of inertia and angular velocity, and the representation of rotational inertia by an inertia tensor.

Typology: Slides

2012/2013

Uploaded on 07/24/2013

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Angular

Momentum

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Moments

The

moment

of

a

vector

at

a

point

is

the

wedge

product.

This

is

applied

to

physical

variables

in

rotating

systems.

Applied

to

momentum

for

angular

momentum

Applied

to

force

for

torque

Moments

are

summed

for

systems

of

particles.

x

1

x

2

x

3

k

j

ijk

i

A

x

A

r

r

A

F

r

N

p

r

J

J

J

N

N

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Law

of

Angular

Inertia

The

time

derivative

of

angular

momentum

vector

is

the

net

torque

vector.

By

the

law

of

reaction,

all

internal

torques

come

in

canceling

pairs.

Only

need

external

torques

N

F

r

dt

J

d

v

m

v

F

r

dt

J

d

p

dt

r

d

dt

p

d

r

dt

J

d

)

(

)

(

)

(

)

(

)

(

)

(

ext

int

ext

F

r

dt

J

d

F

r

F

r

dt

J

d

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Rigid

Body

If

the

positions

of

separate

masses

are

fixed

compared

to

the

center

of

mass

it

is

a

rigid

body

Rigid

body

motion

can

be

expressed

in

terms

of

the

center

of

mass.

Translational

motion

Rotational

motion

r



r



v

CM

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Angular

Momentum

The

angular

momentum

can

be

defined

in

terms

of

the

inertia

and

angular

velocity.

Accounts

for

non

collinear

vectors

J

r

p

j

ij

i

I

J

)

(

,

,

,

,

j

i

ij

k

k

ij

x x x x m I

r r m p r J

     

r

r

r

m

J

2

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Inertia

Tensor

Rotational

inertia

is

represented

by

a

tensor.

Symmetric

tensor

Diagonal

elements

are

moments

of

inertia

Off

diagonal

are

products

of

inertia

)

(

2

3

,

2

2

,

x

x

m

A

)

(

2

3

,

2

1

,

x

x

m

B

)

(

2

2

,

2

1

,

x

x

m

C

C

F

G

F

B

H

G

H

A

I

)

(

,

,

,

,

j

i

ij

k

k

ij

x x x x m I

3

,

2

,

x

x

m

F

3

,

1

,

x

x

m

G

2

,

1

,

x

x

m

H

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