Name ___________________________________________ Date ______________________ Class ________________________
To discover what happens to the total momentum when objects collide.
You might think of conservation as being careful with how much water or gas you use. Or of
conservation of the environment. But conservation can also mean that conditions before and after an event
do not change. These actually are almost the same meaning: when we talk about conserving resources, we
want as little change as possible.
Elastic collision, inelastic collision, momentum
In science we talk about laws of conservation of mass, energy, or momentum. These are all laws that
examine the state or status of a quantity before and after an event and they predict that within a confined
system, the state will not have changed.
Conservation of momentum means that the total momentum of any group of objects before an event is
the same as it is afterwards. No momentum has been lost and none has been gained. Although collisions
may be elastic or inelastic, and even if some balls bounce off at greater velocity than they started with,
energy really is conserved, and total momentum remains constant.
1. Start Virtual Physics and select Conservation of Momentum from the list of assignments. The lab will
open in the Mechanics laboratory.
2. The laboratory will be set up with two balls of same mass on a table. You will perform four experiments
to look at the momentum of the system by looking at the momentum of each ball within the system.
3. Trial 1: Two moving balls. The masses of the balls are the same. The velocities of the balls are also the
same magnitude but in opposite directions, towards each other. The balls start out separated by 10
meters. Click the Start button to watch them collide and click the Pause button a few seconds after they
ounce off each other. Record the final velocity for each ball from the display panel below the table in
the data table below. You can display the velocity of the second ball by clicking on the ball, or clicking
on the Tracking a
ows to change the display.
Trial
1
Mass
(kg)
Velocity
efore (m/s)
Velocity
after (m/s)
Momentum before
(mass × vbefore)
Momentum after
(mass × vafter)
Ball XXXXXXXXXX
Ball XXXXXXXXXX
Total Momentum =
Name ___________________________________________ Date ______________________ Class ________________________
4. Trial 2: One initially moving ball. Click the Reset button to reset the experiment. Using the
Parameters Palette, change the mass of Ball 1 to 15 kg, and the mass of Ball 2 to 5 kg. Uncheck the Balls
Same Mass and Diameter box to be able to change each mass separately. Set the velocity of Ball 1 to 10
m/s and the velocity of Ball 2 to 0 m/s. Click the Start button to watch the balls collide. Click the Pause
utton a few seconds after they bounce off each other. Record the final velocity of each ball in the data
table below.
Trial
2
Mass
(kg)
Velocity
efore (m/s)
Velocity
after (m/s)
Momentum before
(mass × vbefore)
Momentum after
(mass × vafter)
Ball XXXXXXXXXX
Ball 2 5 0
Total Momentum =
5. Trial 3: Two connected balls. Click the Reset button to reset the experiment. Set the velocity of ball 2
to 0 m/s, and change the Elasticity to 0 to make the balls inelastic. Click the Start button to watch the
alls collide. Click the Pause button a few seconds after they bounce off each other. Record the final
velocity of each ball in the data table below.
Trial
3
Mass
(kg)
Velocity
efore (m/s)
Velocity
after (m/s)
Momentum before
(mass × vbefore)
Momentum after
(mass × vafter)
Ball XXXXXXXXXX
Ball 2 10 0
Total Momentum =
6. Trial 4: Choose your own variables. Click the Reset button to reset the experiment. Click on the red
Recording button to start recording data. Choose your own masses and velocities for each ball. Try it
with the balls initially traveling in the same direction, but with one of the balls traveling faster than the
other. Switch the elasticity to 0 again to observe an inelastic collision. Predict what you think the
esulting velocities might be. Test this prediction. Record the data.
Trial
4
Mass
(kg)
Velocity
efore (m/s)
Velocity
after (m/s)
Momentum before
(mass × vbefore)
Momentum after
(mass × vafter)
Ball 1
Ball 2
Total Momentum =
Name ___________________________________________ Date ______________________ Class ________________________
1. On the following grid, graph the momentum of each ball from Trial 4 over the course of the experiment.
When you pause the trial after your observations, a data link will appear in the Lab Book. Click on that
link to display the momentum over time for each ball. Use the #1 p_x data to graph the momentum of
the first ball over time. Your graph should have time on the x-axis and momentum on the y-axis. Also
graph the momentum data of the second ball on the same graph. Label the axes with the variable and its
units. Use a different color for each ball. You will need to scale the graph to fit your data.
2. Is the momentum of the system conserved in each of the trials? Explain?
3. How did the graph help to show the momentum conservation?
4. How can a ball with a small mass have the same momentum as a ball with a large mass?
5. In your own words, how do you describe momentum?