ISCI 1A24 Lecture Notes - Lecture 6: Inverse-Square Law, Orbital Period, Ellipse
12 Jan 2017
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Physics - planetary motion + work & energy. F = mg but g can change on different planets. Reasoned that gravity might be a universal force between any two masses. The strength of the force of gravity must be; Proportional to 1/r2 where r is the distance between them (inverse-square law) Putting this in equation form; fg is proportional to m1*m2/r2. *g is the universal constant = 6. 6784 * 10^-11 m3/kgs2. Newton could immediately use this concept to accurately explain the motions of the moon and the planets. The moon (or any satellite) is in free fall around the earth. At the distance r of the moon : g = g m / r2 (much smaller than at earth) The speed of a satellite or planet in a circular orbit is: Gm/r (r is the radius of the orbit) Planets move in elliptical orbits, with the sun at one focus of the ellipse.
