Work - Analytical Mechanics - Lecture Slides, Slides of Applied Mechanics

In these Lecture slides, the Lecturer has discussed the following key concepts of Analytical Mechanics : Work, Generalized Coordinates, Transformation Rules, Changes, Generalized Velocity, Coordinates Themselves, Generalized, Generalized Force, Constraint Forces, Dependence

Typology: Slides

2012/2013

Uploaded on 07/26/2013

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Work

Generalized

Coordinates

Transformation

rules

define

alternate

sets

of

coordinates.

3

N

Cartesian

coordinates

x

i

f

generalized

coordinates

q

m

Select

f

degrees

of

freedom

Small

changes

in

a

coordinate

can

be

expressed

by

the

chain

rule.

3

1

t

x

x

q

q

N

m

m

1

t

q

q

x

x

f

i

i

polar coordinate example

sin

cos

cos

cos

r

r

x

r

r

r

r

x

cos

sin

sin

sin

r

r

y

r

r

r

r

y

      t t

x

q

q

x

x

i

f

m

m

m i

i

1

Generalized

Force

Force

acting

over

a

small

displacement

is

the

work.

Express

in

generalized

coordinates

Rewrite

the

work

in

terms

of

the

generalized

force

components,

Q

m

Q

t

Last

term

for

time

dependence

i

i

m

m

i m

i

t

t x

q

q

x

F

W

i

i

i

x

F

W

t x

F

Q

q

x

F

Q

t

Q

q

Q

W

i

i

i

t

i

m i

i

m

t

m

m

m

Constraint

Forces

All

the

Qm

are

applied

forces.

No

dependence

on

constraint

coordinates

Not

forces

of

constraint

Constraint

forces

do

no

work

Forces

of

constraint

are

often

unknown.

Newtonian

problem

complicated

by

them

i

m i

i

m

q

x

F

Q

Acceleration

and

Velocity

i

i

i

i

i

i

i

x x m x F W

)

(

The

work

can

be

expressed

by

mass

and

acceleration.

Mass

m

(

i

)

related

to

xi

The

Cartesian

coordinate

is

transformed

to

the

generalized

coordinate.

Use

the

boxed

identity

Work

expanded

in

terms

i

i

m

m

m i

i

i

t

t

x

q

q

x

x

m

W

)

(

i

i

i

m i

i

m

i m

i

i m

i

i

t

t x

x

m

q

q

x

dt d

x

q

x

x

dt

d

m

W

)

( ,

)

(

]

[

m i

i

m i

i

i m

i

q

x

dt d

x

q

x

x

q

x

x

dt d

Kinetic

Energy

The

velocity

can

be

used

to

find

the

kinetic

energy

T

Rearranging

summation

i

i

i

i

m

i

m

i m

i

m i

i

i

dt

t x

x

m

q

q

x

dt d

x

q

x

x

dt d

m

W

,

)

(

]

[

i

i

i

i

m

i

m i i i m i i i m

t

t x x m q x x m q x x m q

dt

d

W

)

(

,

)

(

1 2

)

(

1 2

)]

[

i

i

i

i

m

m

m

m

t

t x

x

m

q

q

T

q

T

dt d

W

)

(

]

[

Lagrangian

Function

Conservative

forces

depend

only

on

position.

Leave

non

conservative

forces

on

the

right

side

of

the

equation

The

quantity

L

T

V

is

the

Lagrangian

This

gives

Lagrange’s

equations

of

motion.

For

f

equations,

2

f

constants

m

m

m

m

m

Q

q

V

Q

q

T

q

T

dt d

m

m

m

m

m

Q

q

V

q

T

q

V

dt d

q

T

dt d

m

m

m

Q

q

V

T

q

V

T

dt d

m

m

m

Q

q

L

q

L

dt d

next

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