Universal Gravitation

Remember Newton's Law of Universal Gravitation

F_g = G(m₁m₂)/r²

Newton stated the law of universal gravitation in terms that applied to the motion of planets about the Sun.

This agreed with Kepler's 3rd law and confirmed that Newton's Law fit the best observations of the day.

All of this works together to get the equation for finding the Period of a planet orbiting the Sun.

How large is the constant G?

Strange as it may seem, it took 100 years from the time of Newton's work for scientists to develop an apparatus that was sensitive enough to measure the force of gravitational attraction.

Cavendish's investigation is often called weighing Earth because it helped determine Earth's mass.

Once "G" is determined , not only the mass of Earth, but the mass of the Sun can be determined.

In addition the gravitational force between any two objects can be calculated using Newton's Law of Universal Gravitation.