Chapter 12: Gravitation Newton’s Law of Gravitation
Gravitational attraction Note: Two particles of different mass exert equally strong gravitational force on each other
Gravitational Forces (I) MM MM ME FG = G r 2 ‘‘Attractive Force” ME
Cavendish balance Cavendish(1798) announced that he has weighted the earth
Average Density of the Earth g = 9.80 m/s2 RE = 6.37 x 106 m ME = 5.96 x 1024 kg rE = 5.50 x 103 kg/m3 = 5.50 g/cm3 ~ 2 x rRock ???
The gravitational force is conservative Note: Work done is Path independent!
Gravitational potential energy Note: The gravitational potential is zero at infinity
Projectile
Projectile
Circular orbit
Kepler’s Laws Each planet moves in an elliptical orbit, with the sun at one focus of the ellipse A line from the sun to a given planet sweeps out equal areas in equal times. 3. The periods of the planets are proportional to the 3/2 powers of the major axis lengths of their orbits.
Geometry of an ellipse
Elliptical orbit