Transcript Day 11
Announcements •Next observing Night is a Dark Sky Night one week from Wednesday on February 22 and then again on Monday February 27 •Be thinking about your project topic. I need to approve your topic before spring break. •Exam 1 will be returned next time. Still grading the essays. Kepler developed three laws of planetary motion based on Tycho’s data on Mars Kepler’s st 1 Law The Law of Ellipses The planets move in elliptical orbits with the Sun located at one focus Major change since everyone that came before had used circles, including Copernicus Kepler’s nd 2 Law The Law of Areas A line drawn from a planet to the Sun will sweep out equal areas in equal time periods Kepler’s Law rd 3 The Law of Harmonies The ratio of the square of the orbital period to the cube of the orbital semimajor axis (the radius) is the same for all the planets Galileo Galilei •1564 – 1642 •First to turn the telescope skyward •Developed new physics to replace the physics of Aristotle •Got into deep trouble with the Catholic Church Galileo’s first major discovery concerned the planet Jupiter Over a week long period in January 1610 he makes observations that prove the existence of four moons orbiting Jupiter. Another of his observations that support the Copernican views is the phases of Venus In late 1632, Galileo’s book Dialogues is banned and he is put on trial by the Inquisition In June 1633 he is found guilty and sentenced to prison. After recanting his views, his sentence is commuted to house arrest If you ask a physicist, Galileo’s most important contributions were in mechanics Newton’s Mechanical Universe Isaac Newton (1643 – 1727) Newton’s home: Woolsthorpe in Lincolnshire Newton’s most important work Newton was 43 years old when the Principia was finally published. Most of the work for it was done when he was in his early 20’s Newton’s First Law: The Law of Inertia An object in uniform motion (straight line at constant speed) will maintain that motion unless acted on by some external force. Newton’s Second Law: The Force Law The acceleration an object experiences is directly proportional to the net force acting on it and inversely proportional to the objects mass. F = ma Newton’s Third Law: The ActionReaction Law For every force there is an equal and opposite reaction force. Newton’s Law of Universal Gravitation Two bodies attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers Newton related the acceleration experienced by a falling apple to that experienced by the moon rEarthmoon 60rEarth 1 amoon 3600 aapple Galileo had measured the acceleration of a falling body near the surface of the Earth. Newton calculated the acceleration needed to keep the moon in orbit (centripetal acceleration). A few colored card questions ClassAction website Renaissance Astronomy module Gravity Fundamentals…options 1 & 3 Gravity Directions…both options Earth Force vs. Sun Force Forces and Motion Discussion Questions: Applying Newton’s Laws 2