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PROBEWARE INVESTIGATION 4  A
Relationship Between Impulse and Momentum
Newton combined an object's mass and velocity
in an expression which he called “quantity of
motion.” We now define this product of mass
and velocity as momentum. From Newton's
second law we see that an object's velocity
changes when it is acted upon by an unbalanced
force. This would also mean then that its
momentum would change. Forces act for a
period of time even though sometimes it is only
for a short moment. The product of force and
time is known as impulse.
Problem
How can you measure the impulse given to an
object by certain forces and how can you
measure the momentum so that you see the
relationship between the two? How can you
measure the momentum in an explosion using
probeware equipment?
Hypothesis
Formulate a hypothesis to explain how impulse
and momentum relate to each other, and to
describe what happens to momentum during an
explosion or other interaction.
2. Record the mass of the dynamics cart.
3. Set up the motion sensor at one end of the
track.
4. Set up the force sensor at the other end of the
track so that the cart can have a magnetic
collision with the sensor. There is a collision
bracket that can be attached to the track for
this purpose. Another way is to put the force
sensor at the very end of the track against a
wall or stand and then put the second
dynamics cart containing the magnets against
the force sensor.
5. Secure the track in such a way that it cannot
move.
6. Push the cart so that it coasts and collides
with the force sensor arrangement with the
computer measuring the velocity of the cart
and the force sensor recording the force of
the collision.
7. Plot graphs showing velocity vs. time and
force vs. time.
Equipment
• computer probeware with two motion sensors
and a force sensor
• dynamics track with two dynamics carts
• sand
Caution
Arrange all electrical cords so they are out of the
way and will not be tripped on.
Place dynamics carts upside down when not in
use so they won't roll off the lab bench.
Prevent the dynamics carts from striking the
motion sensors during the experiment.
Procedure 1 (impulse and momentum)
8. Repeat for different velocities.
Analyze and Conclude
1. Calculate the impulse during the collision by
finding the area under the force vs. time
curve for the collision period.
2. From the velocity vs. time graph find the
change in velocity (v) from before the
collision to after the collision. Multiply the
mass of the cart by v to find the change in
momentum of the cart.
3. Compare the impulse given to the cart to the
change in its momentum.
1. Level the dynamics track.
Copyright © 2002 McGraw-Hill Ryerson Limited
PROBEWARE INVESTIGATION 4  A
Relationship Between Impulse and Momentum (continued)
Procedure 2 (momentum in an explosion)
1. Set up a motion sensor at each end of the
dynamics track. If your probeware does not
support this arrangement, use a photogate
timer near each end of the track.
2. Using the calculator reverse the sensing of
one of the motion sensors so that all
velocities in one direction will be positive
and those in the other direction will be
negative.
3. Put a load on one of the carts and find the
mass of both carts.
4. Cock the spring plunger on one cart.
5. Place the carts close together in the centre of
the track.
6. Create an “explosion” by triggering the
plunger so that the carts move off in opposite
directions while the probeware records the
velocities of each.
7. Repeat using different masses.
Procedure 3 (momentum and an interaction)
1. Raise one end of the track until the effect of
friction is eliminated and the cart will coast
at constant velocity once it is released.
2. Place the motion sensor at the raised end of
the track.
3. Record the mass of the cart.
4. Place about 300 g of sand in a small bag and
find its mass.
5. Give the cart a push so that it coasts down
the track and drop the bag of sand onto it
vertically as the probeware records the
velocity. Make sure that the sand is dropped
vertically with no horizontal velocity
component.
6. Repeat using different velocities and
different masses of sand.
Analyze and Conclude
1. From the graph of velocity vs. time calculate
the momentum of the cart before the sand is
dropped onto it and after the drop.
Analyze and Conclude
1. Determine the momentum of the two carts
before the explosion.
2. What conclusion can you draw based on your
observations?
2. From the velocity vs. time graphs find the
velocity of each cart after the explosion and
calculate the momentum of each keeping in
mind the direction.
3. What law of physics is confirmed by your
conclusion?
3. Determine the total momentum of the carts
after the explosion.
4. What conclusion can you draw from the
experiment?
4. Describe what happens to the vertical
momentum of the sand dropped onto the cart.
5. Using the technical specifications on your
equipment, perform an error analysis on your
results.
Copyright © 2002 McGraw-Hill Ryerson Limited