Phys 2305
Y04st
1
RECALL:
•
Newton’s second law: The vector sum of forces (net force) acting on a body equals its mass
times its acceleration.
m
a
=
X
F
=
F
total
•
It follows that when a body is in equilibrium, the vector sum of the forces acting on it (the net
force) must be zero.
m
a
=
X
F
and
a
=
0
⇒
X
F
=
0
;
in components:
X
F
x
= 0
,
X
F
y
= 0
,
X
F
z
= 0
.
•
(Contact forces; not fundamental) When a body is in contact with a surface, that surface
must exert a force on the body. This force can be represented in terms of a normal component
perpendicular to the surface and a friction component parallel to the surface. The friction force
depends on the character of the surfaces in contact and on whether or not the body is moving
relative to the surface.
f
k
=
μ
k
N
,
f
s
≤
μ
s
N
•
Good systematic problemsolving technique is essential in solving problems in mechanics and
in all other branches of physics. Intuition, analysis, and then precise mathematical formulation
of the problem
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Phys 2305
Y04st
2
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 Spring '08
 TSChang
 Physics, Acceleration, Force, Friction, Mass, Friction Force

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