Elastic Collisions: Kinetic energy is conserved, objects bounce off. | Inelastic Collisions: Kinetic energy is not conserved, energy lost as heat/sound, objects may stick.

Closed System: No exchange of matter/energy, momentum conserved. | Open System: Exchange of matter/energy, momentum may not be conserved.

Momentum is a measure of how much 'oomph' an object has when it's moving; its resistance to changes in motion.

$p = mv$, where $p$ = momentum, $m$ = mass, and $v$ = velocity.

Impulse is the change in an object's momentum caused by a force acting over a period of time.

$J = \Delta p = F\Delta t$, where $J$ = impulse, $\Delta p$ = change in momentum, $F$ = force, and $\Delta t$ = time interval.

A closed system is one where no matter or energy is exchanged with the surroundings; total momentum remains constant.

An open system is one where matter or energy can be exchanged with the surroundings; total momentum may not be constant.

Elastic: Kinetic energy is conserved, objects bounce off each other. Inelastic: Kinetic energy is not conserved, some energy is lost, objects may stick together.

Closed System: No exchange of matter/energy, momentum conserved. Open System: Exchange of matter/energy possible, momentum may not be conserved.

Momentum: measure of mass in motion (vector). Kinetic Energy: energy of motion (scalar).