2
Elastic collisions
We now apply the conservation laws to the interaction of two particles, in particular collisions.
In general, two types of collisions are possible: Elastic and Inelastic. By definition
1. Elastic collisions:
P
i
=
P
f
and
K
i
=
K
f
;
2. Inelastic collisions:
P
i
=
P
f
and
K
i
=
K
f
;
where
K
is the kinetic energy of the system. We begin with a discussion of elastic collisions.
In many occasions it is desirable to choose a coordinate system at rest with respect to the
system’s center of mass (CM). In reality, actual measurements are carried out in a coordinate
system where the observer is at rest, the laboratory (LAB) coordinate system. In the LAB
system, one particle is in motion whereas the struck particle is usually at rest.
In CM, we use the notation that
m
1
is the mass of the moving particle, and
m
2
the mass
of the struck or stationary particle. In the LAB system the velocities of
m
1
are
u
1
=
Initial
(69)
v
1
=
Final
(70)
while in the CM system we use the same notation, but all variables are primed.
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 Spring '10
 RogerMelko
 Kinetic Energy, Momentum

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