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2-6 Galileo Galilei (1564-1642). The first modern scientist. A new step in history of science:. Observations and careful measurements can reveal much about the way the world works. Study of motion. You need to exert a force on an arrow to make it fly .
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2-6 Galileo Galilei (1564-1642) The first modern scientist
A new step in history of science: Observations and careful measurements can reveal much about the way the world works
You need to exert a force on an arrow to make it fly but once it is flying, what makes it carry on? The mysterious angel of motion ?
Inclines Speed increases Speed decreases Speed should not vary
When I perform the experiment, the object comes to a stop. Why? Four centuries later, this is remembered as “Newton’s first law of motion” … There must be a force acting against the motion, slowing it down What could this force be? Friction? Then spreading soap should remove it. Or may be we could use a ball, which has a very small contact surface So if no net force is acting on an object, it moves in a straight line, at constant speed Like a hockey puck!
Conclusion • A force is required to start an object moving, but also to : • slow it down • speed it up • change the direction of its motion
Free fall You drop a marble and a hammer from the top of the Pisa tower. Which reaches the ground first?
Hammer arrives first They reach the ground at the same time
Aristotle would answer: The hammer. Heavy objects fall faster than lighter ones
But Galileo came with an unexpected answer: They reach the ground simultaneously
Galileo’s “thought” experiment: Let’s assume that Aristotle is right. Now tie the hammer and the marble with Scotch tape.
1 - The marble falls slower than the hammer, so it slows down the hammer’s motion 2 – The marble makes the hammer heavier, so the hammer falls down faster Does not make sense!
Hammer arrives first They reach the ground at the same time
Galileo, you made essential discoveries, but this time you are wrong!
The feather reaches the ground last because it is slowed down by air friction On the Moon where there is no air, they would both reach the ground simultaneously
Galilean relativity You are now standing on the lookout of a sailing boat The boat sails at constant speed You drop ball. Where does it fall?
Remember that when the ball is leaving your hand, it has the same speed as the boat…
… so that the ball is not falling vertically, even if you simply dropped it”
“Actually, the ball would hit the deck right below your hand”
Unbelievers? If you dribble a ball in a train moving at constant speed, do you feel any difference with dribbling on the station platform?
The first telescope • refractor Galileo learns that a Dutch lense maker has invented a device that makes distant objects look closer 1609: Galileo constructs its own telescope and adds a stable mount to be able to observe celestial objects
Dark patches on the surface of the Sun (sunspots) that indicate the Sun rotates on its axis with a period of one month 1612
Four moons orbiting around Jupiter A centre of motion can itself be in motion! Why couldn’t the Earth be orbiting the Sun like Jupiter does?
Finally he had a close look at Venus Phases expected with the heliocentric model Phases expected with the geocentric model
Galileo’s heliocentric model Was discussed in Dialogue Concerning the Two Chief World Systems Dialogue between: Simplicio (Aristotle) Salviati (Galileo) Sagredo (layman)
If the Earth were moving around the Sun,a stone dropped from a tower would hit the ground more than 300 m west of the tower Remember the ball dropped on the boat. We do not detect any motion because we move with our planet
If the Earth were moving, the Moon would be left behind. How could the Moon keep up with the Earth’s motion? The moons of Jupiter do
If Copernicus’s model is so simple, it is because it describes reality. The planets do orbit around the Sun Disagreement with the Ptolemaic and Aristotelian views accepted by the Roman Catholic Church
The Pope was quite open minded and interested in Galileo’s work
But Galileo was too audacious He wrote in Italian rather than scholarly Latin He lectured publicly his ideas At the Medicis’ court, Galileo participated in verbal games with religious scholars He was brilliant and enjoyed to ridicule his opponents, increasing the number of his enemies
Feb 1616: The Inquisition declares: « holding the view that the Sun is the center of the universe is heretical » March 1616 : The Congregation of the Index bans Copernicus' book 1624 Pope Urban VIII tells Galileo that he can discuss Copernican theory - so long as he treats it as an hypothesis
Feb 1632:Galileo is stubborn. He decides to print « Dialogue Concerning the Two Chief World Systems » Summer 1632: Distribution is stopped by Pope Urban VIII
April 1633: Galileo appears before the Holy Inquisition
Galileo recants: “Having been admonished by this Holy Office entirely to abandon the false opinion that the Sun is the centre of the world and immovable, and that the Earth is not the center of the same and that it moves…I curse and detest the said errors and heresies, and generally all and every error and sect contrary to the Holy Catholic Church.”
Galileo was allowed to return to his villa in Florence, where he lived under house-arrest until his death
His books were on the Chuch’s forbidden list until 1836 In 1992, Pope John Paul II publicly endorsed Galileo’s philosophy
Galileo’s point of view implied a universe way larger than anything imagined before. Why?
If the Earth is orbiting the Sun, we should observe the parallax of nearby stars If we don’t, it means that even the nearest stars a lot further away than anything believed at that time * 1 AU
Select what you believe to be Galileo’s single most important astronomical observation.
Sunspots Phases of Venus Craters of the Moon Jupiter’s Moons
