Universal Gravitational Constant
What exactly is the gravitational constant? This constant was determined experimentally by physicist Henry Cavendish (1731-1810). His famous experiment consisted of small and large spheres that were attracted to each other by gravity. As the small spheres move towards the large, the rod they are connected to turns. A light beam reflecting of a mirror measures the angle of rotation. By repeating the experiment with different mass and different radius lengths, Cavendish established that the Universal Gravitational Constant is 6.673x10^-11.