Gravity Lecture.pdf

Gravity is everywhere In 1798 Henry Cavendish made his sensitive measurement to determine a numerical value for the constant G. Gravity decreases as altitude rises it?s interesting to follow the density as one proceeds from crust to mantle to core http://www.astronomynotes.com/gravappl/s10.htm Physics of Tides Gravitational potential energy ? Objects changing their distance from earth are also changing their potential energy with respect to earth. A brief history of Gravity Claudius Ptolemy (85 ? 165) Alexandria, Egypt Nicolai Copernic (1473 ? 1543) Poland Johannes Kepler (1571 ? 1630) Germany Kepler?s Laws Kepler?s 1 st Law Kepler: The path of each planet about the Sun is an ellipse with the Sun at one focus. Newton: Gravity gives the centripetal force! Kepler?s 2 nd Law Kepler: Each planet moves so that an imaginary line drawn from the Sun to the planet sweeps out an equal area in equal periods of time Newton: This is explained by angular momentum conservation. Kepler?s 3 rd Law 3 2 1 2 2 1 S S T T ? ? ? ? ? ? ? ? = ? ? ? ? ? ? ? ? Galileo Galilei (1564 ? 1642) Italy Isaac Newton (1643 ? 1727) England Newton?s law of gravity: ?Every particle in the universe attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them. This force acts along the line joining the particles? Albert Einstein (1879 ? 1955) Weightlessness What is the difference between being in ?free fall? and being ?out of the reach of large gravitational forces?? N. Duller PowerPoint Presentation