Space shuttle orbit, ex. 10, p. 92
This is a strength ratio exercise.  How strong is gravity at two different points?  The ratio of distances tells the tale, using two distance measurements:  from the center of Earth to each observation point, one on the surface of Earth and one in orbit.  Here is the standard way of deducing relative strengths from distance information.
  1. 1) Get the ratio of distances, r1:r2
  2. 2) Square the distance ratio, (r1:r2)2
  3. 3) Invert the squared distance ratio, (r2:r1)2.
  4. 4) Strength at location 1:strength at location 2 = (r2:r1)2.
That is how all gravitation and electromagnetic strength ratio problems work.  This is because they are both inverse-r2 forces.
Tuesday, July 10, 2007
Shuttle orbit compared to Earth's surface