1-D Collisions & Momentum
Names:
Video Analysis Lab
Physics
Objectives:


To utilize momentum carts to investigate the nature of different types of collisions
To perform video motion analysis on elastic and inelastic collisions to explore the
principle of momentum conservation graphically and numerically
Materials:

LoggerPro Software

Elastic Collision Video

Inelastic Collision
Video
Introduction
The impulse-momentum theorem relates impulse, the average force applied to an object
times the length of time the force is applied, and the change in momentum of the object:
𝛴𝐹 × ∆𝑡 = ∆𝑝 = 𝑚𝑣𝑓 − 𝑚𝑣𝑖
Here we will only consider motion and forces along a single line. The average force, F , is
the net force on the object, but in the case where one force dominates all others it is
sufficient to use only the large force in calculations and analysis.
For this experiment, a dynamics cart will roll along a level track and collide with a second
cart. Using video technology, you will analyze the collision (before, during and after).
Using Logger Pro to develop velocity-time graphs, you will test the Law of Conservation of
Linear Momentum.
𝑚1 𝑣1𝑖 + 𝑚2 𝑣2𝑖 = 𝑚1 𝑣1𝑓 + 𝑚2 𝑣2𝑓
Note: Save the logger pro file to the “My Documents” folder instead of your student
drive. (There may be issues with using large files over the network.)
Part A: Initial Measurements
Step A-1:
Record the mass of each cart in the table on page 2.
Part B: An Inelastic Collision Visualized
Introduction:
In this section, you will set-up and perform video motion analysis on a completely inelastic
collision to analyze the momentum transfer that occurs during the collision.
Procedure (Completely Inelastic Collision):
Step B-1: Import the video into Logger Pro.
Step B-2: Video Motion Analysis:
a. Resize and move the movie (if needed) for viewability and convenience.
b. Use the QuickTime buttons at the bottom to review the movie.
c. Click on the movie window and select the “Video Analysis” button (righthand corner).
d. Scale the movie using a meter stick as your reference.
e. Select the positions for cart 1 in each frame. If possible, try to get at
least10-20 points before and 10-20 points after the collision.
f. Observe the graph window and select “X” for the y-axis and “time” for
the x-axis.
Analysis:
A-1: Observe the two parts of the position graph. Explain what this graph shows:
A-2:
Apply a linear fit to each portion of the position graph to find the velocity of each
cart just before and just after collision. Record values in the table on page 3
and copy paste your graph below:
A-3:
Calculate the average momentum of Cart 1 and Cart 2 before and after collision.
Record in the table.
A-4:
Calculate the change in momentum (p) for both cart 1 and 2. Record the data.
Object
Cart 1
Cart 2
Mass
(kg)
Before Collision
vaverage
paverage
(m/s)
After Collision
vaverage
paverage
(m/s)
Change in
Momentum (Δp)
Part C: An Elastic Collision Visualized
Introduction:
In this section, you will set-up and perform video motion analysis on an elastic collision to
analyze the momentum transfer that occurs during the collision.
Procedure (Elastic Collision):
Step C-1: Import the video into Logger Pro.
Step C-2: Video Motion Analysis:
a. Begin you video analysis as you did in Part B, setting the scale and
tracking the motion on the inbound cart.
i. Resize and move the movie (if needed) for viewability and
convenience.
ii. Use the QuickTime buttons at the bottom to review the movie.
iii. Click on the movie window and select the “Video Analysis” button
(right-hand corner).
iv. Scale the movie using a meter stick as your reference.
v. Select the positions for cart 1 in each frame. If possible, try to get
at least10-20 points before and 10-20 points after the collision.
vi. Observe the graph window and select “X” for the y-axis and “time”
for the x-axis.
b. After tracking the first cart, you will need to rewind the video and track
the second cart. Do this by adding a point series and collecting data for
cart 2 before and after the collision. The button looks like this.
Analysis:
A-5 Apply a linear fit to each portion of the position graph to find the velocity of each
cart just before and just after collision. Record values in the table and COPY
PASTE this graph with the curve fits below:
A-6 Calculate the average momentum of Cart 1 and Cart 2 before and after collision.
Record in the table.
A-7 Calculate the change in momentum (p) for both cart 1 and 2. Record the data.
Object
Mass
(kg)
Before Collision
vaverage
paverage
(m/s)
After Collision
vaverage
paverage
(m/s)
Change in
Momentum (Δp)
Cart 1
Cart 2
A-8: How does pcart 1 compare with pcart 2?
A-9: What does this imply about the total momentum before, during and after this
particular collision?