1. Module 2

1.22. Module Summary/Assessment

Module Summary and Assessment

Module 2—The Conservation of Momentum in Isolated Systems

Module Summary

 

In Lesson 1 you investigated the momentum in an isolated system during a collision. You verified one of the fundamental laws that govern physical processes, the law of conservation of momentum. In summary, the law states: momentum is “mass in motion" or a measure of how much motion an object has. Expressed as an equation, it is as follows:

 

 

In a collision between two objects, the change in momentum of one object is equal and opposite to the change in momentum of the other object. Expressed as an equation, it is as follows:

 

 

The law of conservation of momentum states that the sum of the momentum in a system before a collision equals the sum of the momentum in the same system after a collision. Expressed as an equation, it is as follows:

 

 

You learned that we can analyze collisions to determine initial velocities or predict final velocities by applying the conservation of momentum.

 

In Lesson 2 you investigated the total kinetic energy of a system before and after a collision and found that kinetic energy is not always conserved. This is a criterion that distinguishes between two types of collisions. Furthermore, the amount of lost kinetic energy can be used to produce a spectrum of “elasticity,” including the following three generalizations for collisions:

  • Perfectly elastic collisions result in the total kinetic energy of the system being conserved. Perfectly elastic collisions generally occur only at the subatomic level.

  • Inelastic collisions involve some loss of kinetic energy, generally as sound or thermal energy. This is a broad range, and most collisions fall within this class.

  • Perfectly inelastic collisions are ones in which the colliding objects stick together upon impact. There is the greatest loss of kinetic energy in this type of collision.

All linear and non-linear collisions are described by one of these three general classifications, including the one analyzed for the module assessment in the form of a crash reconstruction analysis.

 

In Lesson 3 you studied collisions that occur in two dimensions. You verified that the total momentum of an isolated system is conserved during a collision. Specifically, the total momentum in the x direction and in the y direction is also conserved during a collision.

 

Therefore, and .

 

Using this conservation principle, it is possible to analyze two-dimensional collisions, such as those of vehicles that meet in an intersection.

 

Module Assessment

 

Module 2 Project

 

In each lesson you have been working on a crash analysis of the collision between Kathy and Bill. The last part of the analysis was completed at the end of Lesson 3. Submit the entire analysis including answers to all of the questions in the Reflect on the Big Picture sections of Lessons 1, 2, and 3 of Module 2.