**PRELAB**

**VIDEO**
Look at a preview of the lab activities.

**PURPOSE**

To learn about conservation of momentum and kinetic energy by studying different types of collisions.

**EQUIPMENT**
linear air track, DataLogger interface, gliders, two photogates, and weights.

**RELEVANT EQUATIONS**

Momentum of a particle:

p = mvTotal momentum = sum of individual momenta:

p_{tot}= m_{A}v_{A}+ m_{B}v_{B}Kinetic energy:

KE = mv^{2}/2

**DISCUSSION**

In this experiment, you will verify
in practice the conservation principles studied previously in the collision
simulation lab. They are: conservation of momentum (**C of M**) and
conservation of kinetic energy (**C of KE**). In the case where two
bodies collide and move along a straight-line path both before and after
the collision, the conservation of momentum is simply expressed as:

Keep in mind that the vector nature
of the velocities is important here. In motion along a straight line, the
vector direction is indicated with a plus or minus sign. In addition, in
some of the cases you will consider in this experiment, the masses are
two identical gliders, so the two masses are equal, and we can call them
both **m**. This fact simplifies the conservation of momentum equation
considerably:

The other conservation rule applies
only to collisions that can be termed __elastic__. This usually refers
to the condition where no mechanical energy is lost to heat during the
collision. If any or both of the bodies are permanently deformed, that
is, any deformation that occurs during the collision does not "spring back",
then the collision in __inelastic__ and conservation of energy does
not apply. The worst case scenario for this type of collision is called
__completely inelastic__ when the two colliding bodies stick together after
the collision.
The conservation of kinetic energy can be expressed in general as:

An illustration of an elastic collision between two pucks is shown in this
**movie**. Using the conservation of
momentum for any collision, and the conservation of kinetic energy for an
elastic collision permits us to determine one or more unknowns. Usually there
are four variables, the velocities of the two masses both before and after
the collision. For example, in an elastic collision, with two independent
equations (**C of M** and **C of KE**), if we assume that the initial
velocities of the two masses are known, then algebra theory tells us that
we can solve for the two remaining unknowns with two simultaneous equations.
Therefore, we should be able to find the final velocities of the two masses
in the general case. Another example is the completely inelastic collision.
Here we only can apply **C of M** and not **C of KE**, but we also
are dealing with only three variables, since the velocities of the masses
after the collision are the same (they stick together). Thus, if the two
initial velocities are known, we can solve for the one remaining unknown,
the final velocity of the composite body using one equation.

Print out and complete the
**Prelab questions**.