Physics 218 Lecture 3,4

1. Physics 218 Lecture 3,4

2. Galileo Galilei 1564-1642

3. “Father of modern science” Albert Einstein Stephen Hawking: Galileo probably bears more of the responsibility for the birth of modern science than anybody else. Was the first to apply a scientific method: Put forward a hypothesis, verify it by experiment, describe it with a mathematical model Insisted that language of mathematics should describe the laws of nature and experiments should prove it. No place for arguments based on beauty, religion etc.

4. Achievements in physics Verified that free-fall acceleration is independent on masses of bodies. This fact inspired Einstein’s General Relativity. Formulated the Principle of Relativity, which laid the framework for Newton’s laws and inspired Einstein’s Special Relativity. Proposed the Principle of Inertia, which was used (borrowed?) by Newton as his First Law. Found that the period of a pendulum is independent on its amplitude. Legend says that he discovered it by observing swings of a bronze chandelier in the Cathedral of Pisa and using his pulse to measure the time!

5. What he did for astronomy • Was the first to report using the telescope to view the heavens. • Telescope invented in 1604 by Hans Lippershay. • Galileo used the telescope in 1609. Built his own. Two lenses in a metal tube about 4 feet long, diameter = 4 cm (1.6 inches). Magnification 3X to 33X. • His observations between 1609 and 1612 changed our ideas about the universe. • What did he see? • New stars (Milky Way made up of stars) • Mountains and valleys on the moon • Four moons orbiting Jupiter (now called Galilean moons) • Phases of Venus • Sunspots (rotating around the sun about once a month) • The rings of Saturn (sketches. was puzzling; not identified as • rings until about 50 years later.) • Planets are disks, not pinpoints of light like the stars

6. 32X power

7. 0 Major Discoveries of Galileo • Moons of Jupiter (4 Galilean moons) • Rings of Saturn (What he really saw)

8. Major Discoveries of Galileo (2) • Surface structures on the moon; first estimates of the height of mountains on the moon

9. Major Discoveries of Galileo (3) • Sun spots (proving that the sun is not perfect!)

10. Major Discoveries of Galileo (4) • Phases of Venus (including “full Venus”), proving that Venus orbits the sun, not the Earth!

11. Arguments against the geocentric model were so forceful that he came under fire from the Catholic Church and was forced to give a public denial of the heliocentric/Copernican system, and was placed under house arrest for the last 10 years of his life. Science in Italy was dealt a severe blow. The center of scientific investigation shifted to northern Europe. Only in 1992, Pope John Paul II expressed regret for how the Galileo affair was handled.

12. Sentence of the Tribunal of the Supreme Inquisition against Galileo Galilei, given the 22nd day of June of the year 1633 "It being the case that thou, Galileo, son of the late Vincenzio Galilei, a Florentine, now aged 70, wast denounced in this Holy Office in 1615: "That thou heldest as true the false doctrine taught by many, that the Sun was the centre of the universe and immoveable, and that the Earth moved, and had also a diurnal motion: That on this same matter thou didst hold a correspondence with certain German mathematicians.... "That the Sun is the centre of the universe and doth not move from his place is a proposition absurd and false in philosophy, and formerly heretical; being expressly contrary to Holy Writ: That the Earth is not the centre of the universe nor immoveable, but that it moves, even with a diurnal motion, is likewise a proposition absurd and false in philosophy, and considered in theology ad minus erroneous in faith..... "We say, pronounce, sentence, and declare, that thou, the said Galileo, by the things deduced during this trial, and by thee confessed as above, hast rendered thyself vehemently suspected of heresy by this Holy Office, that is, of having believed and held a doctrine which is false, and contrary to the Holy Scriptures, to wit: that the Sun is the centre of the universe, and that it does not move from east to west, and that the Earth moves and is not the centre of the universe: and that an opinion may be held and defended as probable after having been declared and defined as contrary to Holy Scripture; and in consequence thou hast incurred all the censures and penalties of the Sacred Canons, and other Decrees both general and particular, against such offenders imposed and promulgated. From the which We are content that thou shouldst be absolved, if, first of all, with a sincere heart and unfeigned faith, thou dost before Us abjure, curse, and detest the above-mentioned errors and heresies and any other error and heresy contrary to the Catholic and Apostolic Roman Church, after the manner that We shall require of thee. … “ http://www.fordham.edu/halsall/mod/1630galileo.html

13. GALILEO'S ABJURATION I, Galileo Galilei, son of the late Vincenzio Galilei of Florence, aged 70 years, tried personally by this court, and kneeling before You, the most Eminent and Reverend Lord Cardinals, Inquisitors-General throughout the Christian Republic against heretical depravity, having before my eyes the Most Holy Gospels, and laying on them my own hands; I swear that I have always believed, I believe now, and with God's help I will in future believe all which the Holy Catholic and Apostolic Church doth hold, preach, and teach. But since I, after having been admonished by this Holy Office entirely to abandon the false opinion that the Sun was the centre of the universe and immoveable, and that the Earth was not the centre of the same and that it moved, and that I was neither to hold, defend, nor teach in any manner whatever, either orally or in writing, the said false doctrine; and after having received a notification that the said doctrine is contrary to Holy Writ, I did write and cause to be printed a book in which I treat of the said already condemned doctrine, and bring forward arguments of much efficacy in its favour, without arriving at any solution: I have been judged vehemently suspected of heresy, that is, of having held and believed that the Sun is the centre of the universe and immoveable, and that the Earth is not the centre of the same, and that it does move. Nevertheless, wishing to remove from the minds of your Eminences and all faithful Christians this vehement suspicion reasonably conceived against me, I abjure with sincere heart and unfeigned faith, I curse and detest the said errors and heresies, and generally all and every error and sect contrary to the Holy Catholic Church. And I swear that for the future I will neither say nor assert in speaking or writing such things as may bring upon me similar suspicion; and if I know any heretic, or one suspected of heresy, I will denounce him to this Holy Office, or to the Inquisitor and Ordinary of the place in which I may be. I also swear and promise to adopt and observe entirely all the penances which have been or may be by this Holy Office imposed on me. And if I contravene any of these said promises, protests, or oaths, (which God forbid!) I submit myself to all the pains and penalties which by the Sacred Canons and other Decrees general and particular are against such offenders imposed and promulgated. So help me God and the Holy Gospels, which I touch with my own hands. I Galileo Galilei aforesaid have abjured, sworn, and promised, and holdmyself bound as above; and in token of the truth, with my own hand havesubscribed the present schedule of my abjuration, and have recited it wordby word. In Rome, at the Convent della Minerva, this 22nd day of June,1633. I, GALILEO GALILEI, have abjured as above, with my own hand.

14. Galileo Galilei (1564 – 1642) • Invented the modern view of science: Transition from a faith-based “science” to an observation-based science. • Rejected the “old” view (still alive now!) that the only path to true understanding is through religious faith • Observations are correct even if they contradict the Scripture • “The Bible tells us how to go to heaven, not how the heavens go.” From “Astronomy” by M. Seeds

15. Basilica di Santa Croce, Florence

16. Burial place of famous Florentines. Among them: Galilei Michelangelo Machiavelli Rossini Fermi Marconi

17. Free Fall Aristotle said that a heavy body falls faster than a light body. A feather, for example, clearly falls more slowly than a gold coin. But Galileo considered the following paradox. Suppose that one drops two gold coins. They fall at the same rate, according to Aristotle, because they are equally heavy. But now suppose that the coins are connected with a very light thread. This, according to Aristotle, should make them fall faster, because they are now one object that is twice as heavy. But why? How do they know that the thread is there? Since the coins are falling at the same rate when unconnected, neither can pull on the other through the thread to make it fall faster. Galileo carefully analyzed this paradox and concluded that Aristotle must be wrong. In the absence of air resistance (which slows the feather more than the coin) all bodies must fall the same, whether they are heavy or light.

19. A legend says that Galileo dropped cannonballs of unequal weights from the Leaning Tower of Pisa to show that both objects reach ground at the same time. This story is probably not true. In fact, Galileo experimented with balls rolling down a ramp. Galileo experimentally proved that objects fall with the same acceleration independently on their masses. He found a correct mathematical formula describing this motion: the distance traveled by a falling body increases as the square of the time that has passed.

21. Free fall www.glenbrook.k12.il.us

22. Falling with air resistance

23. Gravity is a strange force. It has a unique property: All bodies in the same point in space experience the same acceleration! Galileo, about 1600 m R M

24. Universality of g means that in the freely-falling elevator cabin you don’t feel any effects of gravity! You and all objects around you experience the same acceleration. Vice versa: in outer space you can imitate the effect of gravity by acceleration.

25. Equivalence Principle In 1907, Einstein was preparing a review of special relativity when he suddenly wondered how Newtonian gravitation would have to be modified to fit in with special relativity. At this point there occurred to Einstein, described by him as the happiest thought of my life , namely that an observer who is falling from the roof of a house experiences no gravitational field. He proposed the Equivalence Principle as a consequence:- ... we shall therefore assume the complete physical equivalence of a gravitational field and the corresponding acceleration of the reference frame. This assumption extends the principle of relativity to the case of uniformly accelerated motion of the reference frame.