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



Perfectly elastic collisions:  a collision that results in the total kinetic energy of the system being conserved.   Perfectly elastic collisions generally occur only at the subatomic level.




Perfectly inelastic collision: A collision in which the colliding objects stick together upon impact.  There is the greatest loss of kinetic energy in this type of collision.

   

Recall the collision of Kathy and Bill. Based on the information in this lesson, you may wish to return to Assignment 3 to continue working on the questions. 

Remember to re-save your updated Assignment 3.

At the start of this lesson, you were asked the following essential questions:

  • How can the kinetic energy of the objects in a system before and after a collision be used to categorize the type of collision?

  • What is the fundamental difference between an elastic and an inelastic collision?

  • In a collision between two automobiles, is it better for the occupants if the collision is elastic or inelastic?

The kinetic energy values of all the objects in a system can be used to categorize a collision as elastic, inelastic, or perfectly (completely) inelastic. In the case of elastic collisions, the total kinetic energy of the system before the collision equals the total of the kinetic energy of the system after the collision. In other words, kinetic energy is conserved.  These collisions are rare with regard to the collision of everyday objects because some of the kinetic energy is usually converted to sound, thermal energy, or deformation. This is the fundamental difference between an elastic collision and an inelastic collision.

Assignment 2 (Part Two)

Re-open your saved Assignment 2 file, and complete Part Two.  When you are finished, re-save your document and continue to Lesson 3.