NASA
Nasa: Newton's Theory of "Universal Gravitation"
This site, which is provided for by NASA, discusses the thinking which led Newton to understand universal gravitation.
Science and Mathematics Initiative for Learning Enhancement (SMILE)
Smile: Measuring the Gravitational Constant, G
A demonstration/lab idea for determining the numerical value of the universal gravitation constant using a torsion balance.
Physics Classroom
The Physics Classroom: Newton's Law of Universal Gravitation
States the equation of Newton's law of universal gravitation. States the value of G and uses the equation to solve problems.
Physics Classroom
The Physics Classroom: Cavendish and the Value of G
A short description of how Cavendish measured the value of G - the universal gravitation constant and supported Newton's theory. Illustrated.