Rev. 1
REVIEW SHEET #5:
Impulse, Linear Momentum, Conservation of Linear
Momentum;
Center of Mass
Definitions:
In many situations the net force on an object is not constant and acts only during a short
time interval.
Examples are a ball bouncing off a wall or a baseball bat hitting a ball.
For such situations it is useful to define the
impulse
that the net force
ext
F
∑
r
imparts on
the body during the time interval from t
1
to t
2
:
2
1
t
ext
t
J
F
dt
=
⋅
∑
∫
r
r
(impulse is a vector)
Making the simplifying assumption that the net force is constant and setting
2
1
t
t
t

= ∆
the expression for the impulse becomes
(
29
ext
J
F
t
=
⋅∆
∑
r
r
An object of mass m and velocity
v
r
is defined to have
linear momentum
p
mv
=
r
r
(linear momentum is a
vector)
The ImpulseLinear Momentum Theorem

The change in the linear momentum of
an object during a time interval equals the impulse of the net force that acts on the
object during that time interval:
2
1
J
p
p
p
= ∆ =

r
r
r
r
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 Spring '08
 KOHLER
 Physics, Center Of Mass, Force, Mass, Momentum

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