For those of you who go on to take the second semester course, you will see a clear parallel between calculating the net gravitational force on a particle in the presence of other masses and calculating the net electric force on a charged particle in the presence of other charges.  Coulomb’s Law, which describes the electrical interaction between charges, is very similar in its form to the Universal Law of Gravitation and some of the problems you will encounter with electrical forces should certainly remind you of the problems you will work in this section to calculate the net gravitational force on a point mass.

However, as beneficial as this material will be in providing a solid foundation at the start of next semester, it is also worth pointing out some of the current research that is being done that relies on the Universal Law of Gravitation.  Beginning in 1995, a research group at UCLA has spent over two decades tracking stars as they move around the center of the Milky Way galaxy.  Using their observations and the Universal Law of Gravitation, they were able to show that a supermassive black hole with a mass roughly 4.6 million times greater than the mass of the sun resides at the center of our galaxy.  An animation of the stars orbiting the black hole can be found at the group’s website, http://www.astro.ucla.edu/~ghezgroup/gc/animations.html.