Lecture II – From Galileo to Newton

“What if the Sun be Center to the World, and other Stars
By his attractive vertue and thir own
Incited, dance about him various rounds?
In six thou seest, and what if sev’nth to these
The Planet Earth, so stedfast though she seem,
Insensibly three different Motions move?”
John Milton – Paradise Lost, VIII, 122-130

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A literal rebirth of knowledge in all areas – art, literature,
AND science!
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Led by the “virtuosi”, a segment of society that were patrons of the arts (and sciences)
Educated and influential
Paid for printing of manuscripts
Highly interested in scientific and medical matters
Departure from the traditional support of science by kings/queens/monarchies.

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Born in Pisa in 1564 (same year as
Shakespeare)
Moved to Florence in the 1570’s
Went to University of Pisa to study medicine – ended up studying the pendulum
… later developed a pendulum clock
Questioned the Aristotlean view that heavier objects fell faster than lighter objects … hail storms and inclined planes!
Eventually, he was appointed professor at the University of Padua

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Developed one of the earliest telescopes, based on earlier European designs (20x magnification)
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Studied:
The Moon*
Satellites of Jupiter**
Supernova***
Phases of Venus***
Sunspots***
Helped to verify the Copernican heliocentric model – the way things WERE, not just the mathematical model!!!

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He had to be creative (esp. when writing about things that went against the RC church doctrine)
“Dialogues Concerning the Two Chief World Systems”
(1624)
Three characters – Salviati, Sagredo, and Simplicio
Arguments were presented by Salviati and Simplicio, with
Sagredo as the arbiter
Pope Urban VIII had told Galileo that he could write about Copernican theory, so long as it was presented as a mathematical model
Salviati = Galileo, Pope = Simplicio

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In 1633, he was called to Rome to face the Inquisition
Convicted of heresy, and sentenced to house arrest for the remainder of his life
This was a pretty good outcome – see Giordano Bruno!
Died in 1642 in Florence (at the age of 78!)

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Italian Dominican Friar, philosopher, mathematician, astronomer
Extended Copernican theory to include that:
The sun really WAS the center of the solar system
The sun was actually a star!
The universe contained an infinite number of worlds that were populated by other intelligent beings
Found guilty of heresy in 1600 by the
Inquisition, and was burned alive at the stake … not a good way to go

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In 1633, he was called to Rome to face the Inquisition
Convicted of heresy, and sentenced to house arrest for the remainder of his life
This was a pretty good outcome – see Giordano Bruno!
Died in 1642 in Florence (at the age of 78!)

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Mathematician, philosopher, physicist
“Cogito ergo sum”
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He is incredibly important, because he put for the notions that:
There is a universal mathematics … algebra
There is a universal method … the differential equation
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Mathematics is, quite literally, the language of physics, and thus our models of the appearance of reality are mathematical models

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Born in the country, on a farm – his father died three months before his birth
His mother remarried when he was three, and he lived with his grandmother until he was twelve
She pulled him out of school to work on the farm … fortunately, he was horrible at it!
Went to Cambridge in 1661 … work-study program!
This was at the height of the debate between Aristotlean vs. more modern theories of science
In 1665 … Cambridge closes down.

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He returned to the country, and continued private study
Invented calculus (or at least the idea)
Developed a theory of light and color
Developed a theory that would form the basis for the laws of planetary motion
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He returned to Cambridge in 1667, earned his Master’s degree, and then eventually “inherited” a professorship at
Cambridge

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Over his career, Newton engaged in many nasty correspondences with
Robert Hooke … most notably on the laws that would describe planetary motion
He used his position as head of the
Royal Society to discredit Hooke
In the end, though, he used some of
Hooke’s ideas in formulating his own laws

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In 1678, he suffered a nervous breakdown
Went into seclusion, and began work
(under the advice of Edmund Halley) on his greatest treatise …
Finally, in 1687, he published Philosophiae
Naturalis Principia Mathematica (The
Mathematical Principles of Natural
Philosophy)
This contained, among many other things, Newton’s Laws of Motion

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(I) Without an external force acting upon it, an object will remain at rest, or will continue to move with constant speed
(II) The speed of an object will change in proportion to the amount of external force acting upon it
(III) For every action, there is an equal and opposite reaction
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In addition, he formulated a law of gravity (inverse square law), and together with the above three laws, he could explain the motion of the moon, the planets, as well as objects on earth
“The force of gravity keeps the universe balanced, makes it work, and brings heaven and earth together in one great equation.”

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His fights with Hooke continued, and escalated
He suffered another nervous breakdown in 1693
He continued to use his positions in government and in the Royal Society to attack others, including Leibniz (over calculus)
He never married
He spent his later years writing about religious issues
(occult) … in fact, he wrote more pages on this topic than any other
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“If I have seen farther than others, it is because I have stood upon the shoulders of giants.”

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(i) create a space for it LENGTH – metres , feet, miles, furlongs
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(ii) put stuff in it
MASS – kilograms , pounds, stones
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(iii) let it heat up
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(iv) let it evolve
TEMPERATURE – Fahrenheit, Celsius, Kelvin
TIME – seconds , minutes, hours, eons

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We want to collect data about the universe … what kind of data can we collect?
Masses of things (kg)
How far things move (m)
How hot things are (K)
How fast things move (m/s)
How dense things are (kg/m 3 )
How much energy something has … whoa … wait a minute … what’s energy?

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A very ephemeral concept … not easy to define … we need a definition:
Imagine an object moving with some speed.
Now, imagine that object smashing into a stationary object.
The faster the first object is moving, and the heavier it is, the more ability is has to “move” the second object.
Energy, to a physicist is the measure of the ability to make an object move through some distance … we call this WORK.
We do work by applying a FORCE to an object and making it move through a DISTANCE.
In the example above, we call this type of energy KINETIC
ENERGY … energy of motion.

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Kinetic Energy … motion
 Gravitational Energy … how much work gravity can do
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Thermal Energy … how much work we could do by using the heat contained in an object … associated with vibrational motion of electrons around the atom, and in molecules.
 Atomic Energy … the energy associated with electrons moving around the nucleus of the atom
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Nuclear Energy … the energy associated with the binding of protons and neutrons together in the nucleus
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Almost everything that goes on in the universe has to do with converting one form of energy to another!!!

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No, not the show.
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The version of creating a universe that we described before was really not too far off from what we think happened!
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In the beginning … there was mass, and it had a LOT of kinetic energy
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The mass was in the form of electrons, protons, neutrons, and not much else … how did we get from then to now?
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And God said, “Let there be light.” … hey, what’s light?

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There has been a LOT of debate about this over the centuries!!!!
The answer, currently, is that we don’t really know.
We do know that it is PURE energy.
We also know that visible light is just one “flavor” of this type of energy, which we call electromagnetic energy
Radio, television, x-rays, UV rays, infrared, microwaves are all flavors of EM energy
How did all these get created, when we only started out with matter and kinetic energy?

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So, there was this guy named Albert Einstein …
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He said that it was possible to convert mass into pure
(EM) energy, and vice versa … pretty cool idea!
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He also wrote down this equation that tells us how much energy we can get out of a particular amount of mass
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So, is that where all the light came from? Uhmmm … no.

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When things are assembled together nicely, they have LESS energy than when they are separated. This energy difference is called binding energy
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In other words, to tear apart a hydrogen atom (a proton and an electron), you have to put energy in to do it … that makes sense.
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Conversely, when you let an electron and a proton come together and FORM a hydrogen atom, you get some energy out … how much, I wonder?
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Well, it is a really tiny amount … imagine a Big Mac. Now, imagine a sesame seed on the bun of a Big Mac. Now, imagine diving the sesame seed a trillion times. Then, take one of those pieces, and divide that a trillion times. Think about the number of calories in one of those pieces … that’s what we’re talking about.

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Eventually, after the Big Bang, the universe cooled down, and electrons and protons started to “combine” into hydrogen atoms. When this happened, they released these little bursts of EM energy … where did it go?
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Well, it’s still there!
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After 14 Billion years, that EM energy is now in the form of microwaves that we can see EVERYWHERE in the universe!!! It’s called the Cosmic Microwave Background, and is our best evidence that the Big Bang really happened!