Collision Types

Most text books describe three different types of collisions. In reality, it is more true to say there are two ends of a spectrum (range) of collision types. Regardless of what type of collision occurs, the total momentum of the system will always be conserved if there are no external forces present.

Collision Type	properties or characteristics	examples of collisions
Totally Elastic	No kinetic energy is lost (KE is conserved). Since KE is not lost, no energy can go into heat or sound. Usually involves only collisions where the objects can't touch. No damage caused to either colliding object.	Atomic or nuclear particles with similar charges. Magnets with similar poles facing each other. An "ideal super-ball", but that's just fantasy...like Flubber!
	Less damage or heat created. Less sound created. More damage or heat created. More sound created.	Super-Ball Ball Bearings A well inflated basketball, or any ball that bounces some. An under-inflated basketball, or any ball that doesn't bounce much.
Totally Inelastic	The colliding objects stick together and become one. Involves the greatest loss of Kinetic Energy. (keep in mind that if it loses KE then the energy will need to appear as heat and or sound) The colliding objects usually suffer some kind of permanent damage	A block of soft clay dropped onto a hard floor. A bad car accident where the cars stick together. Two train cars collide and stick together.

Remind yourself that for any of these collisions, the total momentum of the closed system remains the same and the total energy remains the same (it just may change form from KE to heat). Both the Momentum and the Energy are always conserved when dealing with a closed system.

One example of the different types of collisions comes from examining bullets striking blocks of wood.

bullets.gif (17887 bytes)

To the left is a representation of 3 bullets with equal mass running into 3 blocks of wood with equal mass.

The first bullet passes through the block and maintains much of its original momentum As a result, very little momentum gets transferred to the block
The second bullet, expands as it enters the block of wood which prevents it from passing all the way through it. As a result, most of its momentum gets transferred to the block. (This is a totally inelastic collision.)
The third bullet (a rubber bullet) bounces off the block transferring all of it's own momentum and then borrowing some more from the block. This has the most momentum transferred to the block. (This is an elastic collision.)