===== Pre-lecture: Momentum and Momentum Principle =====

  * Changes in motion; you pay attention to how an object changes it position
  * Define momentum - some objects are easier to change their motion than others
    * $\vec{p} = \gamma m \vec{v}$ is a vector concept; points in direction of velocity vector for a system; complete and alway applies
    * Define $\gamma$
    * $\gamma$ starts to matter at high speeds; less than about 300 km/s $\gamma \approx 1$
    * $\vec{p}=m\vec{v}$
  * The motion of a system is governed by the momentum prinicple
    * Big idea: Forces cause changes in a system's momentum; specifically the net force (define momentarily)
    * N1: An object that experiences no net force moves with constant velocity and vice-versa
    * N2 (MP): The quantitative description is $\Delta \vec{p} = \vec{F}_{net}\Delta t$.
      * What is a force...and...the net force?
    * Where the's calculus?
      * This description is an average force over a time interval; if the time interval shrinks, we get that the net force is the derivative of the momentum.
  * Another way to represent: force vs time graphs
    * More calculus area under the curve gives change in momentum