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=====Interactive Lecture on Assumptions about Central Force Motion ( minutes)=====

{{courses:lecture:cflec:central_forces_notes.pdf|Central Forces Notes}} Section 5  

  * Newton's Law Equations are written down for the motion of two interacting particles.
$$m_1\dfrac{d^2}{dt^2}\vec{r}_1=\vec{F}_{1,ext}-\vec{f}_{12}$$
$$m_2\dfrac{d^2}{dt^2}\vec{r}_2=\vec{F}_{2,ext}+\vec{f}_{12}$$
  * Students work in groups to create a list of assumptions that were made in writing these equations
    * only 2 particles
    * same origin
    * masses do not change with time
    * all of Newton's laws apply
      *non-quantum (size)
      *non-relativistic (speed)
  * These equations were added to find center of mass and are now subtracted to find relative motion.
  * Discuss further assumptions that the class will use when dealing with central force problems.
    - that you can ignore external forces since you only care about the relative motion of the particles, i.e., the motion of the particles with respect to the center of mass;
    - the force is central, i.e., the force acts along the line between the two particles and depends only on the distance between them.

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