# Instructional Goals

momentum = mass ´ velocity or Momentum is represented in equations with a lowercase "p" The units of momentum are kgm/s.

Momentum is a vector - it has both magnitude and direction. A slow massive object could have the same momentum as a fast, low-mass object.

Define impulse as the net external force acting on a system for a period of time or  J = FnetDt.  Impulse is represented in equations with an uppercase "J".  The units of impulse are Ns.

n much the same way as W (or Q or R) produces a change in the energy of a system, an impulse acting on a system produces a change in momentum.  pi  +  J  = pf

This is usually expressed as Ft = mv - and is called the impulse-momentum change theorem.

Just as displacement is the area under a velocity-time graph, impulse equals the area under an Fnet vs. time graph.

In an elastic collision (think of perfect superballs bouncing off a wall) both the kinetic energy and the momentum are unchanged. No energy is transferred to the thermal account.

In an inelastic collision (think of a lump of clay hitting and sticking to the wall) momentum is conserved, but some of the kinetic energy is transferred to the thermal account.