Conservation of Momentum Java Lab
Purpose: (1) To demonstrate that momentum is conserved with laboratory measurements; (2) To distinguish between an
elastic and an inelastic collision.
The Principle of Conservation of Momentum
Collisions between two objects obey the Principle of Conservation of Momentum. The total momentum, i.e. the
sum of the products of the mass of each object times its velocity never changes, although the individual terms in the sum
certainly do. This is only true, of course, if the
two objects are effectively isolated from the rest of the universe so that there are no other forces acting on the colliding
objects. In our experiment this is true.
Conservation of Momentum is one of the great laws of nature. Closely related to Newton's Laws, the principle sets
constraints on the possible outcomes of a collision event. Momentum is a vector quantity and the conservation law refers
to all vector components. In this experiment everything moves one dimensionally (horizontally on the track), so velocity
components are not important, but algebraic signs are critical.
We will study different types of interactions:
• Elastic Collisions: The two objects collide and bounce apart almost immediately.
• Completely Inelastic Collisions: The two objects collide, stick together, and move as a single object after the collision.
In our description of a two object interaction, let’s agree to use vo’s for pre-interaction velocities and vf’s for postinteraction velocities. The subscript letters R (Red) and B (Blue) label the two objects.
The law of conservation of momentum asserts:
Equipment:
Computer
Internet Site: http://www.walter-fendt.de/ph14e/
Choose: Elastic and Inelastic Collision
Page 1
Name___________________________
Period________________
Date________________
Procedure:
1. Select Elastic Collision.
2. Towards the bottom on the right-hand side select Velocity.
3. Type in a value for the Mass of Wagon 1 (Red) between 0.1 and 1.0 kg and record it in Data Table #1.
4. Type in a value of 0.2 m/s for the Velocity of Wagon 1 (Red).
5. Type in a value for the Mass of Wagon 2 (Blue) between 0.1 and 1.0 kg and record it in Data Table #1.
6. Type in a value of 0.0 m/s for the Velocity of Wagon 2 (Blue).
7. Click the Start button.
8. Watch the collision then record the Velocities after the collision: that appear on the screen in Data Table #1.
9. Towards the bottom on the right-hand side select Momentum.
10. Without changing any of the values, click the Reset and then the Start button.
11. Watch the collision then record the Momenta before the collision: and the Momenta after the collision: that appear on the screen in Data
Table #1.
12. Click Reset, change values from Steps 3-6, then repeat Steps 7 -11.
Data Table #1
Elastic
Collisions
Mass of
Red Wagon
(kg)
Velocity
of Red
Wagon
before
collision
Momentum of
Red Wagon before
collision
(m/s)
(kg • m/s)
Mass of
Blue
Wagon
(kg)
Velocity
of Blue
Wagon
before
collision
(m/s)
Momentum of
Blue
Wagon
before
collision
(kg • m/s)
1
0.2
0
2
0.5
0
3
0.2
-0.2
4
0.5
-0.2
5
0.5
0.3
6
0.5
0.1
Page 2
Total
Momentum before Collision
Velocity
of Red
Wagon
after collision
Momentum of
Red Wagon after
collision
Velocity
of Blue
Wagon
after collision
(kg • m/s)
(m/s)
(kg • m/s)
(m/s)
Momentum of
Blue
Wagon
after collision
(kg • m/s)
Total
Momentum after
Collision
(kg • m/s)
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
Towards the bottom on the right-hand side select Velocity.
Type in a value for the Mass of Wagon 1 (Red) between 0.1 and 1.0 kg and record it in Data Table #2.
Type in a value of 0.2 m/s for the Velocity of Wagon 1 (Red).
Type in a value for the Mass of Wagon 2 (Blue) between 0.1 and 1.0 kg and record it in Data Table #2.
Type in a value of 0.0 m/s for the Velocity of Wagon 2 (Blue).
Click the Start button.
Watch the collision then record the Velocities after the collision: that appear on the screen in Data Table #2.
Towards the bottom on the right-hand side select Momentum.
Without changing any of the values, click the Reset and then the Start button.
Watch the collision then record the Momenta before the collision: and the Momenta after the collision: that appear on the screen in Data
Table #2.
23. Click Reset, change values from Steps 16-19, then repeat Steps 20 -24.
Data Table #2
Inelastic
Collisions
Mass of
Red Wagon
(kg)
Velocity
of Red
Wagon
before
collision
Momentum of
Red Wagon before
collision
(m/s)
(kg • m/s)
Mass of
Blue
Wagon
(kg)
Velocity
of Blue
Wagon
before
collision
(m/s)
Momentum of
Blue
Wagon
before
collision
Total
Momentum before Collision
Velocity
of Red
Wagon
after collision
Momentum of
Red Wagon after
collision
Velocity
of Blue
Wagon
after collision
(kg • m/s)
(m/s)
(kg • m/s)
(m/s)
(kg • m/s)
1
0.2
0
2
0.5
0
3
0.2
-0.2
4
0.5
-0.2
5
0.5
0.3
6
0.5
0.1
26. Shut down your computer, put it back in the cabinet, and answer the Analysis questions on the last page.
Page 3
Momentum of
Blue
Wagon
after collision
(kg • m/s)
Total
Momentum after
Collision
(kg • m/s)
Name___________________________
Period________________
Date________________
Analysis:
1. Describe what happens during an elastic collision.
2. Was the Total Momentum Before and Total Momentum After in each elastic collision the same? Why or why not?
3. What (variable(s)) causes a wagon to “win” elastic collisions? Explain. (Winning means that it keeps going in the original direction before and after the collision)
4. Describe what happens during an inelastic collision.
5. Was the Total Momentum Before and Total Momentum After in each inelastic collision the same? Why or why not?
6. What (variable(s)) causes a wagon to “win” inelastic collisions? Explain. (Winning means that it keeps going in the original direction before and after the collision)
7. During every collision, which Wagon “felt” a greater:
•
Force
•
Acceleration
•
Impulse
•
Change in Momentum
Page 4