COLLISIONS
Conservation of linear momentum is routinely used to analyze collisions. Although
the objects involved in a collision exert forces on each other during the impact,
these forces are only internal (they occur within the system), and the system’s total
linear momentum is conserved.
The Skinny on CollisionsElastic Collision: In an isolated system, momentum and kinetic energy
are conserved.Inelastic Collision: Momentum is conserved and kinetic energy is NOT
conserved.Perfectly or Totally Inelastic Collision: Momentum is conserved, kinetic
energy is NOT conserved, and the objects stick together.Collisions are classified into two major categories: (1) elastic and (2) inelastic. A
collision is said to be elastic if kinetic energy is conserved. Ordinary collisions
are never truly elastic because there is always a change in energy due to energy
transferred as heat, deformation of the objects, or the sound of the impact.
However, if the objects do not deform very much (for example, two billiard balls
or a hard glass marble bouncing off a steel plate), then the loss of initial kinetic
energy is small enough to be ignored, and the collision can be treated as virtually
elastic. Inelastic collisions, then, are ones in which the total kinetic energy is
different after the collision. An extreme example of inelasticism is completely (or
perfectly or totally) inelastic. In this case, the objects stick together after the
collision and move as one afterward. In all cases of isolated collisions (elastic or
not), conservation of linear momentum states that
total pbefore collision = total pafter collision