A) Start LoggerPro. Then go File,
Open, <Your Physics1 Data Folder>, L08A2-2 (Imp &
Momentum).mbl .
B) Once you have opened the correct file,
the next thing that you must do is to calibrate your force
probe. This will require making two probe readings with
two different and known forces applied to the force probe.
The forces are applied to the probe through the hook ATTACHED
TO THE FORCE PROBE. Follow the steps below to carry out
the calibration:
- Click "Setup" at the top
of the computer screen.
- Click "Sensors".
- Click on the F with the DIN1 below it.
- Click the "Calibrate" tab
above the F.
- Click on "Perform now" off
to the right. (If you don't have "perform now"
showing, you did not make a connection to the ULI when
opening the file. You will have to completely close LoggerPro
and reopen the file.)
- Remove the hanging mass from the force
probe if it is attached. There is now zero force on the
probe.
- Enter zero in the box (replacing the
-5) for the force.
- Click "keep".
- Hook the string for the hanging mass
on the hook of the force probe.
- While holding the cart still, run the
string over the pulley and let the mass hang down, pulling
on the force probe. The force applied to the probe is
now the weight of the mass. That is, (0.052 kg)(9.8 m/s2)
= 0.51 N.
- While still holding the cart with hanging
mass attached, enter 0.51 (N) in the second box that has
appeared on the right (replacing the 5) for the force.
Click "keep".
- The calibration process is complete.
Click on OK to close the calibration box.
C) Check to make sure that the calibration
process has been successful. Failing to do this may result
is a complete waste of time doing everything that follows.
Read the force displayed on the bottom of the screen while
the hanging mass pulls on the stationary cart. The force
should be about 0.5. Remove the string attached to the hanging
mass from the force probe. The force should now be close
to 0. If both of these readings check out, all is well.
If you are having trouble, ask for help.
D) The experiment file has been set up
to record force and motion data at 50 data points per second.
A pull on the force probe will be recorded as a positive
force, and velocity away from the motion detector is a positive
velocity.
E) Be sure your track is level. Use one
of the carpenter's levels and the leveling screw at the
end of the track.
1. Remove the hanging mass from the force
probe. You will not use it again unless you need to recalibrate
your force probe for some reason. Place the cart at least
0.5 meters away from the motion detector. Click the collect
button to begin taking data. When you hear the motion
detector start clicking, give the cart a short pull on
the hook of the force probe, and then let the cart move
freely. While you are collecting data, be sure to hold
the cord to the force probe up off of the table (that
is, don't let the cord drag or pull on the cart), and
keep your hand farther away than the cart from the motion
detector. Sketch the actual velocity versus time and force
versus time graphs on your paper. Write down the approximate
value of the maximum force, the time period over which
the force was applied and the velocity of the cart after
the pull.
2. Examine the graphs carefully. Discuss
how the time interval over which the force is applied
compares to the time interval over which the velocity
changes. Does the velocity change in time periods during
which there is no force applied to the cart? Discuss your
results and answer to the question in terms of the impulse
applied to the cart and the change in the cart's momentum.
3. Use the analysis and statistics features
in the software to measure the average velocity of the
cart before and after the pull. Don't forget to include
a sign. ( To get the average velocity from the graph,
use your mouse to mark the region of interest, then go
to analyze, then statistics and say OK). What is the average
velocity after the pull? What is the average velocity
before the pull?
4. Calculate the change in momentum of
the cart. Show your calculations. The mass of the cart
is 500 grams and the mass of the force probe is about
165 grams.
5. Use the integration routine in the
software to find the area under the force-time graph.
This is the impulse in Ns (To do this, use your mouse
to mark the region of interest, go to analyze, then integral
and say OK) Did the calculated change in momentum of the
cart (question above) equal the measured impulse applied
to cart during the pull? What is the percent difference?
6. Add masses to your cart to make the
total mass twice about twice as large. (Each black bar
is 495 grams.) What is the new mass of your cart and force
probe? Zero the force probe by clicking on the zero button
at the top of the screen. Then click collect, wait for
the motion detector to start clicking and then give the
cart the same pull (to the best of your ability). Be sure
to keep the force probe cord from dragging and keep your
hand out of the way of the motion detector. Try several
times or until you get about the same force and duration
as for your initial try above in step 1.
7. Find the average velocity, as
you did before and calculate the change in momentum. Find
the impulse as before. Is the impulse now about the same
as before or is it different by a factor of 2 (the change
in the mass)? Is the change in momentum about the same
as before or is it different by a factor of 2 ? What is
different by about a factor of 2?
