C:\My Docs\3504\ME3504_S_2012\Syllabus\Handouts 2012\Laws of Mechanics_units_memo_S_2012.doc
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ME 3504/3514
Vibrations /
Systems
Dynamic
R. G. Kirk
8-26-99/ S 2012
Laws of Mechanics
1.
Newton's 1
st
Law
:
Definition of Momentum,
v
m
.
A body at rest or in motion will
remain at rest or in motion unless acted upon by some external force.
2.
Newton's 2
nd
Law
:
Definition of force (or torque).
The sum of all external forces acting
on a body equals the body's time rate of change of momentum.
J
dt
d
J
J
dt
d
T
dt
v
m
d
F
torsion
for
;
)
(
If mass is constant with time
a
m
dt
v
d
m
F
3.
Newton's 3
rd
Law
:
For every action, there is an equal and opposite reaction.
(Use this
to build up system components into system equations of motion.)
4.
Newton's 4
th
Law
:
Mass attracts mass.
Definition of weight.
2
R
m
m
W
b
a
Weight of body for engineering calculation taken as
mg
g
W
mg
W
c
1
or

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