Physics

Etymology of the word “Physics”

Physics comes from the Greek word “υσικά,” title of one of Aristotle’s book;

it is an adjective meaning everything related to nature (“ύσις”.)

Thus, any type of motion as the solar system evolution, all we can investigate with our senses that is related to nature belongs to the field of Physics.

In antiquity, sciences appeared and were prematurely systematized not strictly separated, as in modern times, but they all belonged to the global science of “philosophy;” today, of course, sciences are fully separated and specialized, while philosophy has been reduced to a discipline of the humanitarian sciences.

•Archeological findings reveal that nature and celestial motions had attained the interest of different cultures and nations of the ancient times. Assyrians (the ancient people of Syria nowadays), Babylonians (the inhabitants of Mesopotamia, Iran-Iraq nowadays) and ancient Egyptians had advanced knowledge of astronomy, forming very accurate calendars

Of course, that was not due to scientific research and theoretical interest, but to necessity for their land cultivation; they had observed specific phenomena as for example, the rise of the waters of the Nile which occurred periodically every year and that initiated their knowledge.

The indigenous populations of America, Mayas and Aztecs, also had important astronomical knowledge as demonstrated by their monuments and very accurate (even for our time) calendars (of course their culture reached its peak almost two millenniums after, around 600 AD to 1000 AD!)

The first to present a systematized scientific thought were ancient Greeks, who passed from the everyday problems to theoretical research and, thus, gave birth to sciences. Interestingly, many modern theories converge or even are inspired for future research by theories presented by Greek philosophers: the “Big Bang” theory itself is believed to have many common points with Heraclitus theory of the “Big Fire Sphere” “Sφαῖρος” from which everything initiates and to which everything eventually returns at the end of Times. There is a famous quote by Heraclitus: “Πάντα ῥεῖ καὶ οὐδὲν μένει” (English: Everything flows, nothing stands still); Quantum Physics claim today that even at absolute zero (0°K) quantum-mechanical motion disturbances appear, confirming Heraclitus 2 and a half milleniums after!

(a) Leucippus or Leukippos (Greek Λευκιππος, first half of 5th century BC) There are no existing writings which we can attribute to Leucippus, since his writings seem to have been enfolded into the work of his famous student Democritus. The most famous among Leucippus' lost works were titled Megas Diakosmos (The Great Order of the Universe or The great world-system) and Peri Nou (On mind).A single fragment of Leucippus survives: Nothing happens at random (maten), but everything from reason (ek logou) and by necessity. Leucippus, Diels-Kranz 67 B1

(b) his student Democritus, 460-370 B.C., Democritus argued the eternity of existing nature, of void space, and of motion. He supposed the atoms are originally similar, and that even the human soul consists of globular atoms of fire, which impart movement to the body.

and (c) Epicurus, 341-270 B.C. Epicurus adopted the atomism of Leucippus and Democritus, maintaining that all objects and events—including human lives—are in reality nothing more than physical interactions among minute indestructible particles. His difference was that he believed there is no necessity {Gk. anagkh [anankê]} about any of this, of course; everything happens purely by chance.

One of the most fundamental theories of the ancient Greek thought which is also our modern society point of view about the construction and evolution of nature and space is the theory of “atomism;” the philosophical belief (and experimentally proved nowadays) that everything is composed entirely of various impenetrable, indivisible elements called the “atoms” (“άτομον,” adjective meaning that it can no further be divided, cut). Theory expressed by three philosophers:

The most important scientific contribution of the Greeks to modern times was their knowledge and extensive research on the celestial world; Greek mythology found its place not only on our solar system, with the name of the sun and the six known planets of antiquity, but also to all the constellations of the northern hemisphere and partially the southern, giving names which still hold in our times.

That research was the outcome of their need for navigation (even during night), thus rendering constellations their

secure compass over night. Moreover, their moon-based 12 month calendar (even though the names of the months are completely changed and their duration changed slightly) and seven days weekly calendar was adopted by the Romans, the Christians and was inherited to our modern societies.

Constellation of OrionMap of the Mediterranean Sea

Celestial Sphere

Names of the 7 days:

French: English: planet/God(ess)

Lundi (lune: moon) Monday (moon) Moon(Diane) Mardi (mars) Tuesday (G.Eq.*) Mars/Tyr,TewMercredi (mercure) Wednesday (G.Eq.) Mercury/Woden Wodnes Jeudi (jeus) Thursday (G.Eq.) Jupiter/ThorVandredi (venus) Friday (G.Eq.) Venus/Freya-Frige Samedi (Christian) Saturday (Saturn) SaturnDimanche (Christian) Sunday (Sun) Sun

Interesting enough, Greeks no longer use these names! (They name days after the Bible)

*G.Eq.: German Equivalent

Except from the great contribution of Aristotle, Plato and the other Greek philosophers, an important figure was the astronomer Aristarchus of Samos, (310-230 B.C.) who firstly introduced the idea of the heliocentric solar system at 231 B.C., i.e. that the center of our solar system was not the earth as believed but the sun. To arrive at his conclusion he proved that the bigger of the three bodies, the sun the earth and the moon, is the sun and by far, and therefore the sun is at the center of the solar system.

One last, but not least, reference should be made for the so believed most important and influential of all ancient Greek astronomers, Hipparchus of Rhodes, (190 – 120 B.C.), the person who made the most important contribution before that of Copernicus in the early 17th century A.D. His approach to science ranks him far above other ancient astronomers. It was based on data from accurate observations, and is essentially modern in that he collected his data and then formed his theories to fit the observed facts. Most telling regarding his understanding of the scientific method is the fact that he proposed a theory of the motion of the sun and the moon yet he was not prepared to propose such a theory for the planets. He realized that his data was not sufficiently good or sufficiently plentiful to allow him to base a theory on it. However, he made observations to help his successors to develop such a theory. Most of his work was incorporated in the work of Ptolemy.

Claudius Ptolemaeus, Greek:Κλαύδιος Πτολεμαῖος, English: Ptolemy (90-168)

Greek-speaking geographer, astronomer, and astrologer who lived in the Hellenistic culture of Roman Egypt.

Ptolemy was the author of several scientific treatises, three of which have been of continuing importance to later Islamic and European science. The first is the astronomical treatise that is now known as the Almagest (in Greek Η μεγάλη Σύνταξις, "The Great Treatise"). The second is the Geography, which is a thorough discussion of the geographic knowledge of the Greco-Roman world. The third is an astrological treatise known as the Tetrabiblos ("Four books").

Astronomy

In the Almagest, one of the most influential books of classical antiquity, Ptolemy relied mainly on the work of Hipparchus of three centuries earlier. It was preserved, like most of Classical Greek science, in Arabic manuscripts (hence its name) and only made available in Latin translation in the 12th century. Ptolemy formulated a geocentric model that was widely accepted until the heliocentric solar system of Copernicus. Likewise his computational methods were of sufficient accuracy to satisfy the needs of astronomers and navigators, until the time of the great explorations. They were also adopted in the Arab world and in India. The Almagest also contains a star catalogue, which is probably an updated version of a catalogue created by Hipparchus. It’s list of forty-eight constellations is ancestral to the modern system of constellations, but unlike the modern system they did not cover parts of the southern hemisphere (only the sky Ptolemy could see). The Almagest is also known as the Great Syntaxis of Astronomy.

Other works

In his Optics, a work which survives only in a poor Arabic translation, he writes about properties of light, including reflection, refraction and colour. The work is a significant part of the early history of optics. His other works include Planetary Hypothesis, Planisphaerium and Analemma.

Ptolemy's theoremIf the quadrilateral inscribed in a circle is given by its four vertices A, B, C, and D in order, then the theorem states that:

where the overbar denotes the lengths of the line segments between the named vertices."If a quadrilateral is inscribed in a circle then the sum of the products of its two pairs of opposite sides is the product of its diagonals".The converse of Ptolemy's theorem is also true (In a quadrilateral, if the sum of the products of its two pairs of opposite sides is the product of its diagonal, then it can be inscribed in a circle).

Canon of Kings

The Canon of Kings was a dated list of kings used by ancient astronomers as a convenient means to date astronomical phenomena, such as eclipses. The Canon was preserved by the astronomer Claudius Ptolemy. It is one of the most important bases for our knowledge of ancient chronology. The Canon derives originally from Babylonian sources.

Canon Contents(1) Babylonian Kings, 747-539 BC, (2) Persian Kings, 538-332 BC , (3) Macedonian Kings, 331-305 BC (4) Ptolemies of Egypt, 304-30 BC , (5) Roman Emperors, 29 BC-AD 160

Ptolemy was the last of the circle of ancient scientists. After his work science faced retrogression and decline; the Roman Empire was not particularly interested in scientific work (as in the Hellenistic period), the famous Library of Alexandria was burnt, destroying more than 90% of the written knowledge of Antiquity, and the religion of Christianity appeared as a revolution and resistance to the Roman empire, religion and everything related to the ancient world, including all scientific advancements and forbidding any research or doubt over the “absolute will of the Lord.”

During the Middle Age, the “Dark Ages” in Western Europe, the only light of wisdom were Byzantium -The Eastern Roman Empire- that preserved the rest of the books, continuing the work and philosophy of the Academy of Plato up to the 7th century A.D., and the Arabs; The liberating form of the religion of Islam at that time gave space for scientific research and evolution at these lands once more. An important contribution of the Arabs are the so called “Arabic numbers,” the ones we use nowadays.The numbers were developed in India by the Hindus around 400 BCE, and the Arabs adopted and relayed this system to the West.

For almost 1000 years Aristotle and Ptolemy were the absolute and undoubted truth of the Western populations, with their work known mainly through Arabic translations. The destruction of Byzantium in the middle of the 15th century A.D., forced Greeks from Constantinople and elsewhere in Greece to immigrate towards Italy (Florence, Venice, etc.), bringing books of the ancient Greek philosophers and rendering the ancient philosophers work known to the Western countries, thus initiating (in combination with the invention of press) the beginning of the period known as the Renaissance. People like Galileo Galilei and others started doubting the “absolute truth” of the religion and the Church, and gave birth to what we call nowadays “scientific research and enterprise.” In the following a list of the different chronological steps in scientific thought and the main figures who initiated them, and who led humanity from the “Dark Ages” to our modern way of thinking, is presented.

Celestial Dynamics, Terrestrial Mechanics:Copernicus (“De revolutionibus orbioum coelestium”: “On the revolutions of the heavenly spheres”) (1543)Galileo Galilei (the “Dialogue”) (1564-1642)Kepler Johannes (1571-1630) (“Mysterium Cosmographicum”: “Cosmographic Mystery”)Bacon

The Mechanical Philosophy:Van Helmont (influenced by Paracelsus)Descartes

The Mechanical Science:PascalHuygens (essay “on light”)

The Mechanical Chemistry:ParacelsusNicolas LemeryRobert Boyle

Organization of the Scientific Enterprise:Robert Boyle (definition of the experimental method)Descarte

The Science of Mechanics:Descarte

Newtonian Dynamics:Galileo GalileiNewton

Nicolaus Copernicus (February 19, 1473 – May 24, 1543)

Astronomer who provided the first modern formulation of a heliocentric (sun-centered) theory of the solar system in his epochal book, De revolutionibus orbium coelestium (On the Revolutions of the Celestial

Spheres).

Copernicus was one of the great polymaths of the Renaissance. Mathematician, astronomer, jurist, physician, classical scholar, governor, administrator, diplomat, economist, and soldier. His formulation of how the sun rather than the earth is at the center of the universe is

considered one of the most important scientific hypotheses in history. It mark the starting point of modern astronomy and of modern science,

encouraging young astronomers, scientists and scholars to take a more skeptical attitude toward established dogma.

The Copernican heliocentric system

Copernicus cited Aristarchus and Philolaus in an early manuscript of his book which survives, stating: "Philolaus believed in the mobility of the earth, and some even say that Aristarchus of Samos was of that opinion." Inspiration came to Copernicus not from observation of the planets, but from reading two authors: Hicetas and Plutarch provided an account of the Pythagoreans Heraclides Ponticus, Philolaus, and Ecphantes. These philosophers had proposed a moving earth, which did not, however, revolve around a central sun.

It has been argued that in developing the mathematics of heliocentrism Copernicus drew on, the Greek and the Islamic tradition of mathematics and astronomy.

Copernicus' major theory was published in the book, De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) in the year of his death, 1543.

He held that the Earth is another planet revolving around the fixed sun once a year, and turning on its axis once a day. He arrived at the correct order of the known planets and explained the precession of the equinoxes correctly by a slow change in the position of the Earth's rotational axis. He also gave a clear account of the cause of the seasons: that the Earth's axis is not perpendicular to the plane of its orbit. But while Copernicus put the Sun at the center of the celestial spheres, he did not put it at the exact center of the universe, but near it.

His model had a large influence on later scientists such as Galileo and Johannes Kepler, who adopted, championed and (especially in Kepler's case) sought to improve it. The Copernican system can be summarized in seven propositions, as Copernicus himself

The seven parts of Copernicus' theory are:

1. There is no one center in the universe

2. The Earth's center is not the center of the universe

3. The center of the universe is near the sun

4. The distance from the Earth to the sun is imperceptible compared with the distance to the stars

5. The rotation of the Earth accounts for the apparent daily rotation of the stars

6. The apparent annual cycle of movements of the sun is caused by the Earth revolving around the sun

7. The apparent retrograde motion of the planets is caused by the motion of the Earth, from which one observes

Kepler's laws

Kepler inherited from Tycho Brahe, court mathematician to Emperor Rudolf II, a wealth of the most accurate raw data ever collected on the positions of the planets.

The difficulty was to make sense of it. The orbital motions of the other planets are viewed from the vantage point of the Earth, which is itself orbiting the sun. As shown to the graph, this can cause the other planets to appear to move in strange loops.

Johannes Kepler (December 27, 1571 – November 15, 1630)

German mathematician, astronomer, astrologer, and an early writer of science fiction stories, a key figure in the scientific revolution.

He is best known for his laws of planetary motion, based on his works Astronomia nova, Harmonice Mundi and the textbook Epitome of Copernican Astronomy.

He finally arrived at his three laws of planetary motion:

Kepler's elliptical orbit law: The planets orbit the sun in elliptical orbits with the sun at one focus.

Kepler's equal-area law: The line connecting a planet to the sun sweeps out equal areas in equal amounts of time.

Kepler's law of periods: The time required for a planet to orbit the sun, called its period, is proportional to the long axis of the ellipse raised to the 3/2 power. The constant of proportionality is the same for all the planets.

He was the first astronomer to successfully predict a transit of Venus (for the year 1631). Kepler's laws were the first clear evidence in favor of the heliocentric model of the solar system. Isaac Newton eventually showed that the laws were a consequence of his laws of motion and law of universal gravitation.

Kepler concentrated on trying to understand the orbit of Mars, but he had to know the orbit of the Earth accurately first. So, he used Mars and the Sun as his baseline, since without knowing the actual orbit of Mars, he knew that it would be in the same place in its orbit at times separated by its orbital period. Thus the orbital positions of the Earth could be computed, and from them the orbit of Mars.

In 1604, Kepler observed a supernova in the constellation Ophiuchus, the first and only ever since in the Milky Way.

Kepler also made fundamental investigations into combinatorics, geometrical optimization, and

natural phenomena such as snowflakes, always with an emphasis on form and design. He was also one of the founders of modern optics, defining for example antiprisms and the Kepler telescope.

In addition, since he was the first to recognize the non- convex regular solids (such as the stellated dodecahedra), they are named Kepler solids in his honor.

Kepler also was in contact with Wilhelm Schickard, inventor of the first automatic calculator, whose letters to Kepler show how to use the machine for calculating astronomical tables.

Remnant of Kepler's Supernova SN 1604

Galileo Galilei (February 15, 1564 – January 8, 1642)

Italian physicist, astronomer, astrologer, and philosopher who is closely associated with the scientific revolution. His achievements include improvements to the telescope, a variety of astronomical observations, the first and second laws of motion, and effective support for Copernicanism. He has been referred to as the "father of modern astronomy," as the "father of modern physics," and as the "father of science." Galileo's career coincided with that of Johannes Kepler.The work of Galileo is considered to be a significant break from that of Aristotle.

Scientific methods

In the pantheon of the scientific revolution, Galileo Galilei takes a high position because of his pioneering use of quantitative experiments with mathematically analyzed results. There was no tradition of such methods in European thought at that time. Galileo also contributed to the separation of science from philosophy or religion. These are the primary justifications for his description as the "father of science".

Galileo showed a remarkably modern appreciation for the proper relationship between mathematics, theoretical physics, and experimental physics.

Famous quote:

Epur si muoveAnd yet it does move

Astronomy

Galileo first noted an observation of the moons of Jupiter. This observation upset the notion of that time that all celestial bodies must revolve around the Earth. He firstly discovered Jupiter's four largest satellites (moons): Io, Europa, Callisto, and Ganymede. He observed that Venus exhibited a full set of phases similar to that of the Moon. These observations of the phases of Venus proved that it orbited the Sun and lent support to (but did not prove) the heliocentric model.

For example:

- He understood the mathematical parabola, both in terms of conic sections and in terms of the square-law. - He asserted that the parabola was the theoretically-ideal trajectory, in the absence of friction and other disturbances. - He recognized that his experimental data would never agree exactly with any theoretical or mathematical form, because of the imprecision of measurement, and because of irreducible friction, et cetera.

He was one of the first Europeans to observe sunspots, which formerly had been attributed (impossibly) to a transit of Mercury, and he was also the first to report lunar mountains and craters, whose existence he deduced from the patterns of light and shadow on the Moon's surface.

He also observed the Milky Way, previously believed to be nebulous, and found it to be a multitude of stars packed so densely that they appeared to be clouds from Earth. He also located many other stars too distant to be visible with the naked eye.

Finally, Galileo observed the planet Neptune in 1612, but did not realize that it was a planet and took no particular notice of it.

Galileo• At age 19, Galileo discovered the pendulum,

the basis for later clocks• Galileo questioned Aristotelian physics and

performed many of his own experiments, especially with gravity; his work on physics summarized in De Moto

• Most optical telescopes used today derive from the two types of telescopes developed in the 17th century by Galileo and Newton, which amateur and professional astronomers use today

Physics

Galileo's theoretical and experimental work on the motions of bodies, along with the largely independent work of Kepler and René Descartes, was a precursor of the Classical mechanics developed by Sir Isaac Newton. He was a pioneer, at least in the European tradition, in performing rigorous experiments and insisting on a mathematical description of the laws of nature.He performed experiments involving rolling balls down inclined planes, which proved that: falling or rolling objects (rolling is a slower version of falling, as long as the distribution of mass in the objects is the same) are accelerated independently of their mass.

He determined the correct mathematical law for acceleration: the total distance covered, starting from rest, is proportional to the square of the time. He also concluded that objects retain their velocity unless a force — often friction — acts upon them, refuting the generally accepted Aristotelian hypothesis that objects "naturally" slow down and stop unless a force acts upon them. Galileo's Principle of Inertia stated: "A body moving on a level surface will continue in the same direction at constant speed unless disturbed." This principle was incorporated into Newton's laws of motion (first law).

He also noted that a pendulum's swings always take the same amount of time, independently of the amplitude. c

He is lesser known for being one of the first to understand sound frequency.

He also put forward the basic principle of relativity, that the laws of physics are the same in any system that is moving at a constant speed in a straight line, regardless of its particular speed or direction. This principle provided the basic framework for Newton's laws of motion and is the infinite speed of light approximation to Einstein's special theory of relativity.

Galileo's writings

- Two New Sciences 1638 Lowys Elzevir (Louis Elsevier) Leiden (in Italian, Discorsi e Dimostrazioni Matematiche, intorno a due nuoue scienze Leida, Appresso gli Elsevirii 1638) - Letters on Sunspots 1613 - The Assayer (In Italian, Il Saggiatore) 1623 - Dialogue Concerning the Two Chief World Systems 1632 (in Italian, Dialogo dei due massimi sistemi del mondo) - The Starry Messenger 1610 Venice (in Latin, Sidereus Nuncius) - Letter to Grand Duchess Christina 1615

THE SCIENTIFIC REVOLUTION

NEW DIRECTIONS IN ASTRONOMY & PHYSICS

GALILEO GALILEI (1564-1642)

Constructed first telescope

Described motion of bodies on earth

Isaac Newton• Kepler's Laws were a revolution in

regards to understanding planetary motion, but there was no explanation why they worked

• That explanation would have to wait until Isaac Newton formulated his laws of motion and the concept of gravity

• Newton's discoveries were important because they applied to actions on Earth and in space

• Besides motion and gravity, Newton also developed calculus Newton (1642-1727)

Some terms• Force: the push or pull on an object that in some way

affects its motion• Weight: the force which pulls you toward the center of the

Earth (or any other body)• Inertia: the tendency of an object to keep moving at the

same speed and in the same direction• Mass: basically, the amount of matter an object has

• The difference between speed and velocity– These two words have become identical in common language, but in

physics, they mean two different things– Speed is just magnitude of something moving (25 km/hr)– Velocity is both the magnitude and direction of motion (35 km/hr to

the NE)

Newton's First Law• Newton's first law states: An object at rest will remain at

rest, an object in uniform motion will stay in motion - UNLESS acted upon by an outside force

• This is why you should always wear a seat belt!

Outside Force

Newton's Second Law

• Acceleration is created whenever there is a change in velocity– Remember, this can mean a change in magnitude AND/OR

direction

• Newton's Second Law states: When a force acts on a body, the resulting acceleration is equal to the force divided by the object's mass

• Notice how this equation works:– The bigger the force, the larger the acceleration– The smaller the mass, the larger the acceleration

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Newton's Third Law• Newton's Third Law states:

For every action, there is an equal and opposite reaction

• Simply put, if body A exerts a force on body B, body B will react with a force that is equal in magnitude but opposite direction

• This will be important in astronomy in terms of gravity– The Sun pulls on the Earth

and the Earth pulls on the Sun

Isaac Newton (1642-1727)

• Possibly the greatest scientist who ever lived - born on the day Galileo died

• math/physics/astronomy• author of Principia Mathematica in

1687– bringing together Galileo’s discoveries

about motion on Earth and Kepler’s discoveries in the heavens

– to do so he had to develop calculus

• explained heavenly motion that was tied to observed motion on Earth.

Isaac Newton

• Provided a synthesis superior to Aristotle

• notion of inertia - only have to explain change

• Three Laws of Motion

Nature and nature’s laws lay hid in nightGod said, “Let Newton be.” and all was light - Pope.

1 Bodies move in straight lines unless impeded (inertia)

2 Every action has an equal and opposite action

3 every body attracts every other body with a force proportional to the distance between

Isaac Newton (1643 - 1727)

-Wrote “Principia Methematica” which contained mathematicalDescriptions of how the world works (up to the speed of light, asEinstein later proves…)

Law 1: Every object continues in its state of rest or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.  

Law 2: The acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object.  

Law 3: Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

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To explain the motion of the planets, Newton developed three ideas:

1. The laws of motion2. The theory of universal gravitation3. Calculus, a new branch of mathematics

Newton solved the premier scientific problem of his time --- to explain the motion of the planets.

Isaac Newton

“If I have been able to see farther than others it is because I stood on the shoulders of giants.”

--- Newton’s letter to Robert Hooke,perhaps referring to Galileo and Kepler

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Isaac Newton• Mathematical theories explained the

observed motions of the planets. • Considered the greatest scientific

genius until Einstein.• 1684-wrote his major work,

Mathematical Principles of Natural Philosophy

• Theory of gravitation. – Planets bound to the sun by gravitation – Basic force of gravitation and – proved that it explained the motions of

the planets.

Newton’s Beliefs

• 1665: Newton developed calculus

• 1664-1666: Discovered that light is made up of different colors by passing sunlight through a prism

• 1666: Began to develop the theory of gravity

• 1687: Wrote a book on gravity and the laws that make objects move---Principia

Newton and the Apple - Gravity

• After formulating his three laws of motion, Newton realized that there must be some force governing the motion of the planets around the Sun

• Amazingly, Newton was able to connect the motion of the planets to motions here on Earth through gravity

• Gravity is the attractive force two objects place upon one another

The Gravitational Force

• G is the gravitational constant – G = 6.67 x 10-11 N m2/kg2

• m1 and m2 are the masses of the two bodies in question

• r is the distance between the two bodies

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Gravity - Examples• Weight is the force you feel due to the gravitational force

between your body and the Earth– We can calculate this force since we know all the variables

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Gravity - Examples• What if we do the same calculation for a person standing on

the Moon?– All we have to do is replace the Earth's mass and radius with the

Moon's

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Gravity - Examples• If gravity works on any two bodies in the universe, why don't

we all cling to each other?– Replace the from previous examples with two people and the distance

with 5 meters

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Physics: Isaac Newton • English scientist who used the scientific method in science and

mathematics • He was a below average student at the University of Cambridge that

was helped by a tutor who recognized his talent• Newton studied the works of Copernicus and Galileo• In 1665, the plague forced Newton back to rural family farm• There he continued to study and created his theory of gravity• In 1687, Newton published his theories of gravity, etc. in his book

Mathematical Principles of Natural Philosophy aka Principia in which he expanded the theories of Copernicus, Galileo, and Kepler-explained Newton’s theory of universal gravitation-Newton developed calculus in order to prove his theory of gravity

The legend is that Newton saw an apple fall in his garden, thought of it in terms of an attractive gravitational force towards the earth, and realized the same force might extend as far as the moon.

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Newton’s Theory of Universal GravitationNewton and the Apple

(The apple never fell on his head, but sometimes a stupid person will say that, trying to be funny.)

Newton asked good questions the key to his success.

Observing Earth’s gravity acting on an apple, and seeing the moon, Newton asked whether the Earth’s gravity extends as far as the moon.

Newton Cont.

Original copy of Newton’s Principia

Replica of Newton’s Refracting telescope

“To explain all nature is too difficult a task for any one man or even for any one age. `Tis much better to do a little with certainty, and leave the rest for others that come after you, than to explain all things.” - Newton

“...from the same principles, I now demonstrate the frame of the System of the World”Principia Mathematica. Hypotheses non fingo.

“I feign no hypotheses”Principia Mathematica.

If I have seen further it is by standing on the shoulders of giants.

Isaac Newton, Letter to Robert Hooke, February 5, 1675

Newton’s Findings

Newton developed calculus, new kind of math

• Used calculus to predict effects of gravity

• German philosopher Gottfried von Leibniz also developed calculus at same time

• Each accused the other of plagiarism

• Historians believe it was simple case of independent discovery

Isaac Newton and Universal Physics

• The implications of Newton’s law were enormous for he demonstrated with one universal law, mathematically proved, that all motion in the universe, from the movements of the planets to an apple falling off a tree, could be explained

• This Newtonian synthesis created a new cosmology in which the world was largely seen in mechanistic terms

• Would remain the dominant cosmology until Einstein’s concept of relativity

Revisions to Kepler's 1st Law

• Newton's law of gravity required some slight modifications to Kepler's laws

• Instead of a planet rotating around the center of the Sun, it actually rotates around the center of mass of the two bodies

• Each body makes a small elliptical orbit, but the Sun's orbit is much much smaller than the Earth's because it is so much more massive

Revisions to Kepler's 3rd Law

• Gravity also requires a slight modification to Kepler's 3rd Law

• The sum of the masses of the two bodies is now included in the equation

• For this equation to work, the masses must be in units of solar mass (usually written as M)

• Why did this equation work before?

21

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aP

Remember - for this equation to work:

P must be in years!

a must be in A.U.

M1 and M2 must be in solar masses

Michael Faraday: 1791 – 1867AD

• English• Attended the lectures

at the Royal Institution

• 1825: discovered benzene when looking at the ingredients of oil from a dead whale

• Did experiments with electricity

• In 1831, Faraday discovered electromagnetic induction, the principle behind the electric transformer and generator.

• discovery was crucial in allowing electricity to be transformed from a curiosity into a powerful new technology.

• During the remainder of the decade he worked on developing his ideas about electricity.

• He was partly responsible for coining many familiar words including 'electrode', 'cathode' and 'ion'

Michael Faraday

Henry Cavendish

• Experimented with electricity

• Tested the electric current by giving himself shocks and noting the pain he felt

• In 1747, Henry Cavendish started measuring the conductivity (the ability to carry an electrical current) of different materials and published his results.

Henry Cavendish• Cavendish had the ability to make a seemingly limited

study give far-reaching results. • An example is his study of the origin of the ability of

some fish to give an electric shock. He made up imitation fish of leather and wood soaked in salt water, with pewter (tin) attachments representing the organs of the fish that produced the effect.

• By using Leyden jars (glass jars insulated with tinfoil) to charge the imitation organs, he was able to show that the results were entirely consistent with the fish's ability to produce electricity.

• This investigation was among the earliest in which the conductivity of aqueous (in water) solutions was studied.

Henry Cavendish: 1731 – 1810 AD

• British• Was worth over one

hundred million pounds• Son of a Lord and the

grandson of the Duke of Devonshire

• Spent most of his life doing science experiments at home alone

• He discovered a whole range of new gasses

• In 1776 he added acid to marble and the gas that was given off was called fixed air.

• He then dripped acid onto iron, and another gas was given off. It seemed that this gas was lighter than air and burnt so easily, so he called it “fire air.”---What we know now as hydrogen.

Cavendish

• Cavendish was so shy that he never told anyone about his discoveries.

• It was not until 100 years later when James Clerk Maxwell came across his notebooks.