Skip Navigation

University of Nebraska–Lincoln

Transportation Systems Engineering

Teacher Resource Center

Lesson Overview
Lesson Title:
Momentum and Impulse in Car Crashes

Teachers:
Mr. Jeremy Scheffler (Primary)

Brief Description:
Students will use momentum and impulse to analyze collisions.

Topics Introduced:
Impulse-Momentum Theorem

Transportation, Distribution, and Logistics Curriculum Framework Components Addressed:
Transportation Systems/ Infrastructure Planning, Management and Regulation
Health, Safety and Environmental Management
Suggested Grade Levels:
11th Grade
12th Grade

Subjects:
Science
Standards Taught:
8.3.2 Science 2003
12.3.4 Science 2003

Lesson Information
Learning Expectations:

Students determine an object's change in momentum using its mass and a velocity vs. time graph
Students determine the impulse an object receives using a force vs. time graph.
Students will learn that an object's change in momentum is equal to the impulse it receives.

Plan Of Action:

This lesson assumes that students are able to define and calculate momentum and impulse, including finding impulse using the area under a force vs. time graph. Part I is intended to be an inquiry-based activity for students to learn the impulse-momentum theorem. Part II is an activity for students to utilize their discovery in an engineering application. This lesson assumes the use of Vernier sensors to collect the data and Logger Pro software to analyze the data.

Part I
Set up an inclined track with a motion detector at one end and a force sensor at the other and collect real-time data as a cart rolls down the track and collides with the force sensor at the end of the track. The force sensor will produce a force vs. time graph, and the motion detector will produce a velocity vs. time graph.
Examine the velocity graph to determine the velocity of the cart immediately before and immediately after the collision. Using these values and the mass of the cart, students should be able to calculate the cart's change in momentum.
Examine the force vs. time graph and select the interval during the collision. Use the integral function to calculate the impulse on the cart during the collision.
Repeat data collection and calculations for different speeds, different carts, etc. until students are convinced that the impulse and change in momentum should be equal in magnitude.

Part II
After establishing that the impulse on an object is equal to its change in momentum, discuss different ways to achieve the required impulse for a car colliding with a wall (larger force, shorter time; smaller force, longer time; etc.).
Students will be modeling this type of collision with a cart carrying an egg passenger inside of a baby food jar mounted to the cart.
Determine the threshold speed that the cart can collide with a wall without breaking the egg. Start slow and increase the speed incrementally until the egg breaks.
Have students in small groups make modifications to either their cart, the wall, or both with different materials to allow the cart to collide at the threshold speed without breaking the egg. Modifications to the cart model automobile safety features, and modifications to the wall model roadside safety devices.
Have each group test their design at the threshold speed. If the egg survives, increase the speed until the egg breaks to assess the performance of their design.
Discuss the different designs and why they did or did not work.

Data Set Used:

Data is collected by the sensors and graphically displayed in real-time and can be analyzed using Logger Pro.

Materials Needed:

Dynamics carts and track
Vernier force sensor and motion detector
Computer with Logger Pro software
Scale

Eggs
Baby food jars
Bubble wrap
File folders
Aluminum foil
Ziploc bags

Scissors
Tape

Preparation Period:

If the teacher has adequate experience using the sensors and software, it should take 30-60 minutes to set up the equipment and test several collisions to ensure that the results are consistent with the concept being taught.

Implementation Period:

This lesson takes approximately one 45-50 minute class period during a unit on momentum.

Science, Math, Engineering and / or Technology Implications:

Momentum and impulse are covered in a first-year physics course. Integrals are covered in an introductory calculus course, but explaining that the term "integral" simply refers to the area on the graph makes it accessible to all students that have a basic understanding of geometry. Using vehicle collisions to relate these concepts expose students to engineering applications and lead to discussions of safety advancements made possible by improving technology.

Unexpected Results:

Using data collected by sensors in real-time can lead to some unexpected results. For each collision, the change in momentum and impulse calculated from the graphs should be equal, but usually differ at least a little. With some practice, it is possible to get the values to consistently be sufficiently close to one another.

Considerations for Diversity in Education:

Visual learners benefit from watching the collision occur and seeing the real-time data generated in graphical form, and kinesthetic learners benefit from the hands-on construction phase of the lesson.


Lesson Files
Sample Data
Screen shot of sample data collected for a collision.
[size: 55621] [date uploaded: Mar 16, 2011, 5:18 pm ]

Impulse-Momentum (Logger Pro 3.6.1)
Logger Pro file for data collection using a motion detector and force sensor.
[size: 56567] [date uploaded: Mar 16, 2011, 5:19 pm ]

Some video files may require Adobe Flash to open or view.
Download Adobe Flash Player