This lab is outlined on p. 3-37 of the Physics Lab Manual.
The report is to be a readable record of what you did
in lab.
Someone reading it should be able to understand what went on.
- The collisions must take place at low speed (less than
0.4 m/s) if you are to have much hope of seeing momentum
(and KE in elastic collisions) conserved.
- (The impact point is above the CM, so some torque is
exerted on each cart. If a cart 'digs in' at all to the track, system momentum
will not be conserved.)
- The cart bumpers must be placed as close to the track
as possible to help with the 'impact point' problem. (Use
the lower of the two holes on the air carts, not the upper for the bumpers)
-
- Set the air supply on at least '3' (and be ready to go
to '5' if needed)
- Use unequal cart masses by placing 2 50-g masses on one
of the carts.
-
- Put a brief derivation in the report showing that
if linear momentum is conserved in a collision the change in momentum (delta-p)
for one cart is equal and opposite to the momentum change of the other
cart.
-
- Use the '2-channel' version of the sonic ranger program.
-
- Begin by having both carts on the track fairly stationary,
one about 0.7 m from the pinger and one about 1.4 m from the pinger.
- Both cart positions should show up as straight lines
on the graph at the correct distance.
-
- For each good run, one partner should do four
line fits, one for each line on the graph. Do not fail to write
the equations in your lab book. Then the other lab partner should do
another four line fits. (2 for the velocities before collision and
2 for the velocities after the collision)
-
- Calculate and record the change in momentum of each
cart. Do this for each run before going on and doing anything else. Put
this information in your lab book.
-
- Before saving this run to a file , assign an uncertainty
to each cart velocity before and after the collision. This can be done
if the partners' fits are somewhat different. But if both fits are very
close, go back and fit a maximum slope that one might reasonably assign
to each line. Then the uncertainty in velocity will be the difference between
the best and maximum slope velocity.
-
- Bare minimum data
- One good data set for an 'elastic' collision (either
overtaking or head-on)
- One good data set for an inelastic collision (either
overtaking or head-on)
- Full set of data: two good data sets of elastic and two
good sets of inelastic data.
-
- Analysis of Data
- Be sure to show one sample calculation for each type
you are doing.
- Put momentum and KE of each cart before and after each
collision in a table
- Make a table of total KE and total momentum
before and after each collision.
- Put the change in momentum for each cart in each
collision in a table.
- Estimate the uncertainty in momentum for each cart as
the mass times the uncertainty in velocity. Determine the uncertainty in
the momentum change for each cart in each collision.
- Summarize how much total KE was gained or lost in each
collision.
- Summarize how much total momentum was gained or lost
in each collision
- Summarize how the momentum changes compared for the carts
in each collision.
- The previous 3 items could possibly go in one table.
- Work out whether the momentum changes were equal and
opposite within the calculated momentum uncertainties.