Law of Conservation of Momentum LCM
Materials:  air track, two gliders, two photogates, masses, neodymium magnets, clay
Procedures
1.  Set up the air track and photogates using neodymium magnetic bumpers on the gliders to provide a nearly elastic collision.  Be sure the air track is level, otherwise an external force (mgSin2) is present.
2.  Mass m₁ and m₂.  Record the lengths L1 and L2 of each glider (usually 0.01 m) through the photogate.
3.  Set both photogate timers to GATE mode, then press the RESET button.
4.  Place glider₂ at rest between the photogates.  Give glider₁ a gentle push towards glider₂.
[IMPORTANT: the collision must occur after glider₁ has passed completely through photogate₁. After the collision, the gliders must be fully separated before either glider interrupts a photogate.]
Record four time measurements:
    t_1i   the time that glider₁ blocks photogate₁ before the collision.
    t_2i   the time that glider₂ blocks photogate₂ before the collision (zero if glider₂ starts at rest).
    t_1f   the time that glider₁ blocks photogate₁ after the collision (zero if it stops between the photogates.)
    t_2f   the time that glider₂ blocks photogate₂ after the collision.
5.  Repeat Steps 3 and 4 for one more situation when glider₂ has a greater mass than glider₁.  If glider₁ bounces back, you will need to determine the t_1f .
6.  Add a sesame seed-sized slice of silicated soil to one of the gliders for the inelastic collision.
7.  Set both photogates to GATE mode, and press the RESET button.
8.  With glider₁ as the only glider with a timing interrupter,  place glider₂ at rest between the two photogates.  Give glider₁ a gentle push towards glider₂, recording the following times:
   t_1i   the time that glider₁ blocks photogate₁ before the collision.
    t_1f   the time that glider₁ blocks photogate₂ after the inelastic collision.
9.  Repeat Steps 7 and 8 for one more situation of different mass on either glider.

Analysis
1.  For each time measurement, calculate the corresponding glider velocity.
2.  Use your measured and calculated values to calculate p_i and p_f. for all collisions performed.  Be care of +/- velocities and +/- momenta.
3.  State the LCM.  Was momentum reasonably conserved?  What are some sources of error in this lab?
4.  Define the terms elastic and inelastic collisions.