Gravity Animation  This animation shows motion produced by
setting intial positions and velocities of two bodies and then
letting gravity do the rest. The objects were defined thusly:
The gravitational constant of G = 6.67x10**-11 was used. The
animation was viewed from (0 0 400). 500 time slices were
computed with every tenth time slice displayed (i.e., ten
samples per frame). The motion was produced by, for each time
slice for both objects, updating the force, computing
acceleration, calulating average velocity, updating position,
and then updating velocity.  animation.gif (110996 bytes)