§A. A polish astronomer in the 16th Century, realized that our model of our solar system worked much better if we put the Sun at the center and not the Earth.

§B. He is the father of the notion of our Solar §system. (Helios was the Sun god) §C. He dispelled the notions of the (Geos = Earth)

A. Hired by Tycho Brahe, he took the mountains of data pulled together by Tycho over his life and developed Three Laws.

§B. Keps First Law: Each planet moves around the Sun in an elliptical orbit with the Sun as one Focus.

§C. Keps Second Law: A line drawn from any planet to the Sun sweeps out equal area arcs given equal amounts of time.

§D. Keps Third Law: The square of periods of the planets is proportional to the cube of their distances from the Sun. §T 2 = R 3

§A. Any object that has mass exerts a force on other objects of mass. §B. Force = §G m 1 m 2 /d 2 §C. A.K.A.: the Inverse Square Law

More Weightlessness In fact. Gravity does not produce weight! The floor produces weight. Both people are in a gravitation al field.

Ocean Tides p150 Equal forces to the right means Jell-O ball stays spherical. Forces shown here cause left side to lag behind. The left side is further from moon and is not pulled as strongly toward moon.

Spring tides : Neap tides : The earths tilt means that this person has a lower high tide than this person. Tides in the Earth and the atmosphere work the same way.

Tides on the Moon p154 The key thing is that the moon acts like a pendulum. This part of the moon swings back and forth trying to line up with the Earth. Why does the moon always face us?

The Gravitational Field Inside a Planet p155 First, the outside field lines: Now, the inside: Last, the in and the out -side

Einsteins Theory of Gravitation p157 Albert says that the moon is NOT pulled to the Earth. The moon orbits because the surface it travels on is tilted toward the Earth.

Einsteins Theory of Gravitation p157 Albert says that the moon is NOT pulled to the Earth. The moon curves because the surface it travels on is tilted toward the Earth.

Black Holes p157 Their gravitational field is so strong that even light can not escape! A collapsing star with Superman standing on its surface. Because of F=Gmm/d 2 When the star collapses to ½ its radius, the weight quadruples. When the star crushes its matter to a few hundred kilometers, that may be the last we see of it. Only gravity, charge and angular momentum remain. Things orbit it and spiral inward.

Universal Gravitation p 159 As far out as we can see, matter seems to obey Newtons law of gravitation: F=Gmm/d 2. Neptune and Pluto were discovered by using the law. The activities of distant galaxies seem to obey the law. BUT, the universe is expanding too fast!!