Diagram by Roger Breum
       Click here to see a diagram
      by Mike Falls.  | 
    This
      development relates to what is called the simple pendulum. 
      This consists of a pendulum with a rod of length l (L) to which a mass m
      is attached at one end.  The simplifying assumptions are made that
      the mass of the rod is negligible, no external forces act on the system,
      and there is no damping.  The displacement angle is measured from the
      vertical as shown in the diagram on the left and is considered positive
      when measured to the right of OP and negative when measured to the
      left of OP.
         
      The acceleration in the direction of motion
      (tangent to the circular path) of the mass at the end of the rod of the
      pendulum will be 
        
      The force in the direction of motion will be 
        
      In the diagram we see that the magnitude of the
      tangential component of the force due to the weight W is 
        
      The differential equation governing the position
      of the mass at the end of the rod in terms of theta is found by equating
      the two representations of the tangential component of force. 
        
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