Title: Circle of Knowledge
Type: Lesson Plan
Subject: Physics – Momentum Conservation and collisions
Grade Range:11-12
Description: Impulse & Momentum. Conservation of momentum , Elastic and Inelastic collisions
Duration: 90+ Minutes
Author(s): Rama Balachandran

Instructional Unit Content


Content Area Standard   AP Physics- Momentum Conservation and Collisions TAG Standard
Advanced Communication skills-8, Creative thinking & Creative problem solving skills, Higher Order Critical thinking skills


The focus of this lesson is to give students an opportunity to apply concepts of conservation of momentum and collisions to safety features in automobiles and traffic systems and see how the physics principles can be applied to real life situations. They would then use the knowledge gained to problem solve a real life situation in the Accident reconstruction Challenge.   

Enduring Understanding(s)

At the end of this lesson the student will understand that

a.       Total momentum of an isolated system where no external force acts is conserved and that exchange of momentum can take place within the system.

b.      Impulse is the change in momentum  of an object.

c.       The elastic/inelastic  nature of collisions is related to the amount of kinetic energy lost by the system during a collision

d.      How these principles are applied in automobile safety features and in traffic systems.

Essential Question(s)

How can the principles of momentum conservation and collision be applied to

the design of safety features in automobile systems and traffic systems?


Concept(s) to Maintain

An uncancelled force is only required to change the state of motion of an object.
Another way of understanding action – reaction forces is through the transfer of momentum within a system while conserving the total momentum.
Some collisions result in loss of kinetic energy and the degree of loss in kinetic energy decides the nature of collisions.

Evidence of Learning

What students should know:

a.       Conservation of Momentum is an universal principle  b.       The impulse exerted is equal to the product of force and time and is equal to the change in momentum brought about by the force.

c.        Collisions in which the total kinetic energy is conserved are called elastic collisions and those in which kinetic energy is not conserved are called inelastic collisions.


What students should be able to do:

a.       Apply conservation of momentum to decide on probable outcomes of a collision in one and two dimensions   

b.      Apply impulse- change in momentum theorem to situations

c.       Determine the elastic nature of collisions and calculate the loss in energy

d.      Apply concepts learnt to explain how safety features in automobiles and traffic systems operate

e.       Understand and apply the scientific process to accident reconstruction situations that reflects a good understanding of concepts and the ability to examine a situation from different perspectives and come to a judgment.

Suggested Vocabulary

Elastic and Inelastic Collisions

Procedure(s)Phase 1:  Sparking the Discussion (Hook)
  1. Show the class statistics on the trend of crash fatalities in road accidents in the recent years and how it has come down over the recent years. Pose the question “ What do you think is the cause of the reduction in traffic fatalities over the years ?  Students would recognize one of the very important reasons as cars of today being equipped with better safety features. Divide the class into four groups. Ask each group to make a word splash naming all of the automobile safety features and highway safety features that they can recall as a group. Use a poster and ask each group to name one in turns until you get all of them on the poster. Initiate a discussion on how these features work and what principles of physics apply into the working of these devices.
  Phase 2:  Acquiring Content Needed to Participate in Discussion 

1.       Pose the essential (focus) question:  How has automobile safety improved over the years and how do the physics principles apply to the safety features? Activate prior knowledge by having students name any three principles/laws/phenomenon that they have learnt that can directly apply to the working of these safety features.

2.        Students will use prior knowledge to complete the worksheet on identifying the elastic nature of collisions and apply momentum conservation principle to situations similar to real life car crashes. On completing the worksheet, as a class students will discuss to decide which outcomes are probable and based on the outcome , the elastic nature of the collision.

3.       Students will participate in a class discussion of relating these principles to the working of safety features (both passive and active) in automobiles and highway systems. The discussion will be facilitated with video clips from the video – physics of car crash and computer simulations of automobile safety features.

4.       Students will also be assigned a homework assignment which requires them to consolidate their ideas and understanding on any three safety features ( assigned) and present one of it to class.  

Phase 3:  Kindling the Discussion5.       Students will use their notes and the Questioning Cube to answer and have small group discussions.  6.       In whole group, students will participate in a discussion driven by the following questions: 

Pros and cons of airbags

How safety rating impacts car buying

Working of truck escape ramps

Reducing impact force in collisions  

 Phase 4:  Synthesis Activity7.       Students will  be divided into  groups of three . Each group will appoint a recorder to record all computations neatly, an insurance agent who will collect all the facts and organize the information and a presenter  who will present the case and argue in favor of their client. Each group will work on the Accident reconstruction Challenge by applying the principles they have learnt to solve the problem. On completing the reconstruction, each group may take the side of either of the parties involved and present the case in  favor of their client  with supporting arguments.   8.       Summarizing Activity Problem design : Design a problem that integrates as many concepts as you can in this unit into a situation that involves a sport. Make sure your numbers are realistic and you have just sufficient data to solve the problem. Solve your problem and show the method.


Anchor Text(s): Wilson & Buffa – Physics textbook

Simulations of safety features to be used in discussion

Physics of car crashes – video to be used in discussion

 Handouts:Handout 1:  Conservation of Momentum – worksheetHandout 2:  Accident Reconstruction Challenge Handout 3:  Questioning Cube