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Starvard University · Scientific Revolution
Watch the old universe give way: Galileo's telescope and falling balls, then Newton's laws and one gravity for the falling apple and the moon alike.
Hello, my name is Finn, and I'm going to help you understand this course.
Here it is, explained like you are 10:
Long ago, clever people thought the earth sat still in the middle of everything, and the sun, moon, and stars went around it on perfect circles. Then a man named Galileo pointed a new spyglass at the sky and saw mountains on the moon and tiny moons circling Jupiter. He also rolled bronze balls down a ramp and timed them with water dripping from a jar, because he had no stopwatch. Later, Isaac Newton explained the moon and a falling apple with one single rule. This course tells that story with simple experiments you can try on your kitchen table.
The Scientific Revolution was not one discovery. It was a new habit: check it yourself. Instead of asking only what the old books said, Galileo measured how balls actually roll and how pendulums actually swing, and wrote down numbers anyone could test. Newton then took the measurements of Galileo and others and found laws so general that they describe a rolling ball, a swinging pendulum, the tides, and the moon in the same language.
You will meet the old system fairly first, because Aristotle and Ptolemy were no fools: their universe explained a great deal and predicted the planets well enough for calendars and navigation. Understanding what it got right makes it clear why the new evidence mattered, and why honest people argued hard before changing their minds. Bring a ramp, a piece of string, and two balls of different weights. By the last lesson you will have repeated, in miniature, the experiments that changed the world. Along the way you will learn Newton's own rules of reasoning, the short list of cautions he placed at the front of his argument about gravity, because the revolution was as much about how to think as about what the sky contains.
The whole course in brief
What you will be able to do after this course
The eight lessons
Lesson 1
For well over a thousand years, educated people in Europe pictured the universe the way the Greek philosopher Aristotle had described it. The earth sat at the centre, still and heavy. Around it turned great transparent spheres carrying the moon, the sun, the planets, and finally the fixed stars. Earthly stuff was made of earth, water, air, and fire, each seeking its natural place, which is why, in Aristotle's physics, a heavy stone falls faster than a light one: it is hurrying home to the centre.
The astronomer Ptolemy, working in Alexandria in the second century, turned this picture into mathematics. His system put each planet on a small circle, an epicycle, whose centre travelled around a larger circle centred near the earth. It sounds clumsy, yet it predicted where planets would appear well enough to serve calendars, sailors, and astrologers for some fourteen centuries.
This old universe was not stupid. It matched what the eye sees every day: a still earth, a moving sky. Overturning it would take more than a clever idea. It would take new instruments, new measurements, and observers willing to trust them over tradition.
Lesson 2
In 1609 Galileo Galilei, a professor of mathematics at Padua, heard reports of a Dutch spyglass that made distant things look near. He worked out the lens arrangement for himself, built instruments far stronger than the toys being sold, and then did the decisive thing: he pointed his telescope at the sky and published what he saw, in a short book of 1610 called Sidereus Nuncius, the Starry Messenger.
The moon came first. Through the telescope its surface was not the smooth, perfect orb the old philosophy required. Galileo saw bright points appear in the dark part near the boundary of light and shadow, and read them correctly as mountain peaks catching the sun, with shadows stretching beside them, just as on earth. Then, in January 1610, he watched small stars beside Jupiter change places night by night and realised they were four moons circling Jupiter, a centre of motion that was not the earth. The telescope also resolved the Milky Way into countless stars too faint for the naked eye.
None of this alone proved the earth moves. But a moon with mountains was not a perfect heaven, and moons around Jupiter broke the rule that everything circles the earth.
Lesson 3
Aristotle had taught that falling speeds are proportional to weight: his example, quoted by Galileo, says a hundred pound iron ball falling a hundred cubits lands before a one pound ball has fallen a single cubit. Galileo answered that if you drop them together, they arrive at the same moment, apart from a couple of finger breadths caused by the air. His deeper problem was measurement: falling is too fast to time with the instruments of 1600.
His solution fills the most famous pages of his Two New Sciences. Dilute the fall. He took a wooden board about twelve cubits long, cut a straight groove in its edge, lined it with smooth parchment, raised one end, and rolled a hard, round bronze ball down the channel. For a clock he used a large vessel of water with a thin pipe: the water that ran out during each roll was weighed on an accurate balance, and the weights gave the times. Repeated a full hundred times, the results never varied by more than a tenth of a pulse beat.
The law the numbers revealed is beautiful. Distances grow as the squares of the times: in double the time, four times the distance. In successive equal moments, the distances follow the odd numbers, one, three, five.
Lesson 4
The pendulum gave Galileo a second clock and a second surprise. In the Two New Sciences his spokesman describes hanging weights of lead and of cork on strings of equal length and setting them swinging. The cork, being light, is stopped sooner by the resistance of the air, yet while both swing, their vibrations take the same time. The bob's weight does not set the pace.
Neither is the size of the swing. Pull the lead aside through fifty degrees and it describes a wide arc, then a smaller, then a smaller still, yet each vibration, whether of ninety, fifty, twenty, or four degrees, occupies the same time. The swing slows as the arc shrinks in exactly the proportion needed to keep the timing steady. This sameness, called isochronism, later made the pendulum the heart of accurate clocks.
What does change the period is length, by a square root rule Galileo states precisely: the times of vibration are as the square roots of the lengths. To make one pendulum swing twice as slowly as another, make its string four times as long. A ninefold string gives three vibrations of the short one for each of its own, a trick that can even measure an unseen height by counting swings.
Lesson 5
Galileo died in 1642. In 1687 Isaac Newton, a professor at Cambridge, published the Principia, the most influential science book ever written, and near its start he set down three axioms, or laws of motion, on which everything after them rests. They are short enough to learn by heart, and this course will state them in Newton's own sense.
Law one: every body perseveres in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed on it. A spinning top keeps spinning until the air and friction stop it; planets, meeting far less resistance, keep their motions far longer. Law two: the alteration of motion is proportional to the force impressed, and happens in the direction of that force. Double the force, double the change. Law three: to every action there is always opposed an equal reaction. Press a stone with your finger, Newton says, and the finger is also pressed by the stone.
Three plain sentences, yet between them they govern a thrown ball, a recoiling cannon, and the planets themselves. The revolution now had its grammar.
Lesson 6
Newton opened the third book of the Principia with rules of reasoning: admit no more causes than are true and sufficient, and assign the same causes to the same effects, whether stones falling in Europe or in America. Then he applied them to the boldest question of all: is the force that holds the moon in its orbit the same force that pulls a stone to the ground?
His test, the famous moon test, was a sum. The moon sits about sixty earth radii away, and circles us in about twenty seven days and eight hours. If gravity weakens as the square of the distance, then at the moon it should be sixty times sixty, or thirty six hundred times weaker than at the surface. Newton computed how far the moon falls toward the earth in one minute under that weakened pull, scaled the answer to the surface, and got the distance a heavy body here actually falls in one second: about fifteen Paris feet, confirmed by Huygens' pendulum measurements. The numbers matched.
The conclusion followed: every particle of matter attracts every other, weakening with the square of the distance. One gravity moves the moon, the tides, the planets, and the apple.
Lesson 7
You can repeat the heart of this revolution with household things, safely. First, Galileo's ramp. Prop a smooth board or a length of guttering at a low angle, mark equal time beats by tapping a steady rhythm or filming with a phone, and let a ball roll. Note where it is at each beat: the distances should grow roughly as one, three, five, the odd number rule, and the total distance as the square of the time. A phone's slow motion setting makes the counting easy.
Second, the pendulum. Tie a heavy washer or a stone to a string, swing it gently, and time twenty swings with your phone. Then swing it wider and time again: the period stays the same. Use a heavier or lighter weight: still the same. Now double the string and compare; to double the period you will need four times the length, exactly Galileo's square root rule.
Third, the falling test from the first day of the Two New Sciences. Drop a heavy ball and a light ball together from shoulder height onto a cushion, and listen: one thud, not two, unless the light one is so fluffy that the air holds it back. Record your numbers; Galileo repeated his a hundred times.
Lesson 8
This revolution is often told as a simple war between science and faith. The record is more interesting, and fairer to everyone, than that. The facts about Galileo should be stated plainly: his book the Dialogue, published in 1632, argued for the earth's motion; in 1633 he was tried in Rome, found vehemently suspect of heresy, and required to renounce the teaching. He spent the rest of his life under house arrest, and it was there, in those quiet years, that he wrote the Two New Sciences you have been reading in this course. He died in 1642, a Catholic to the end.
Newton, a generation later, was a deeply religious man. The Principia itself ends with a meditation on God as eternal, infinite, and governing all things, and Newton wrote at length on Scripture as well as on motion. Nor was the church simply an opponent of astronomy: churchmen kept calendars, built observatories, and preserved and taught the old astronomy for centuries, and many supported the new observations.
The real change was a method. Careful observation and measurement became a new way of knowing, open to anyone willing to test a claim. That method and religious faith have been held together by many, and argued over by many, ever since.
Sources
This course is taught from classic texts that are free for anyone to read. Every method in the lessons traces back to one of these books.
Graduation
You began under a still earth at the centre of perfect spheres, and you finish with a universe run by laws you can test on a kitchen table. That is the real inheritance of Galileo and Newton: not a list of answers, but the confidence that honest measurement beats argument from authority. Keep experimenting, keep your notes, and congratulations on finishing The Scientific Revolution.
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A note on accuracy: Much of what you read at Starvard was created with help from AI agents, working alongside people. We check what we can, but we cannot guarantee that everything here is true, current, or complete. If something really matters, your health, your money, a grade, a job, please verify it with a trusted source before you rely on it.