Aritstotle: 384-322 BCAritstotle: 384-322 BC

Aristotle was the student of Plato who was the student of Aristotle was the student of Plato who was the student of

Socartes. Socartes.

Aristotle was an accomplished individual whose work would Aristotle was an accomplished individual whose work would

influence the course of history:influence the course of history:

1)1) Teacher – Most Famous Student : Alexander the GreatTeacher – Most Famous Student : Alexander the Great

2)2) First BiologistFirst Biologist

3)3) CosmologistCosmologist

4)4) Physicists - Developed Aristotelian Mechanics Physicists - Developed Aristotelian Mechanics

5)5) PhilosopherPhilosopher

AristotleAristotle

Aristotle was a Aristotle was a keen observerkeen observer of of naturenature. By . By lookinglooking

at natureat nature, he attempted to , he attempted to deducededuce the the workingsworkings of of

naturenature. The . The weaknessweakness of Aristotle and his followers of Aristotle and his followers

was the was the complexitycomplexity of the world. Unlike Galileo and of the world. Unlike Galileo and

modern scientistsmodern scientists who build who build controlled experimentscontrolled experiments

which are which are designeddesigned to to restrictrestrict the the number of thingsnumber of things

which might which might changechange (temperature, pressure, volume, (temperature, pressure, volume,

etc.), Aristotle’s followers worked with systems etc.), Aristotle’s followers worked with systems

where hundreds of things changed. where hundreds of things changed.

Aristotelian MechanicsAristotelian Mechanics

1)1) According to Aristotle, all According to Aristotle, all objectsobjects on Earth have a on Earth have a natural motionnatural motion (rest) and a (rest) and a preferred locationpreferred location in the in the universe.universe.

2) A 2) A forceforce (push or pull) is (push or pull) is requiredrequired to to causecause an an object on Earth to object on Earth to movemove or leave its or leave its natural locationnatural location. .

3) Applying a 3) Applying a forceforce to an object to an object gives the objectgives the object ““impetusimpetus.” As the object .” As the object movesmoves, it , it usesuses up up impetusimpetus. . once the object is once the object is out of impetusout of impetus, the object , the object returnsreturns to to restrest at its at its natural locationnatural location..

Aristotelian MechanicsAristotelian Mechanics

4) According to Aristotle, the universe is composed of 4) According to Aristotle, the universe is composed of five elements (different types of mater):five elements (different types of mater):

EarthEarth WaterWater AirAirFireFire EatherEather

5) 5) Outer spaceOuter space was was filledfilled with with EatherEather, a fluid through , a fluid through which the stars and planets traveled with no which the stars and planets traveled with no resistance. resistance.

6) All 6) All object on Earthobject on Earth were were composedcomposed of of variousvarious amountsamounts of the of the remainingremaining four elementsfour elements..

Aristotelian MechanicsAristotelian Mechanics

7) The Earth is a stationary sphere at the center of the 7) The Earth is a stationary sphere at the center of the universe. universe.

8) The natural place of each element in the universe 8) The natural place of each element in the universe

was determined by observation:was determined by observation:

Earth

Water

Air

Eather

Fire

Aristotelian MechanicsAristotelian Mechanics

Example: According to Aristotle, when we burn a log, Example: According to Aristotle, when we burn a log,

we release fire and air that was contained in the log. we release fire and air that was contained in the log.

The smoke and fire rise because the natural location The smoke and fire rise because the natural location

of fire and air is above that of earth.of fire and air is above that of earth.

Falling Body PredictionsFalling Body Predictions

1)1) Heavier objects fall toward the Earth at a greater Heavier objects fall toward the Earth at a greater

rate since they have more Earth element.rate since they have more Earth element.

Falling Body PredictionsFalling Body Predictions

2) Each object falls to the Earth at a constant speed.2) Each object falls to the Earth at a constant speed.

0

2

4

6

8

Aristitelian Mechanics

0

2

4

6

8

10

12

0 1 2 3 4 5

Time (seconds)

Dis

tan

ce

(M

ete

rs)

CopernicusCopernicus

Platonic ideas including the Ptolemaic solar system Platonic ideas including the Ptolemaic solar system

dominated for over 1500 years. dominated for over 1500 years.

Nicolaus Copernicus (1473-1543) was a polish monk Nicolaus Copernicus (1473-1543) was a polish monk

who didn’t find the Ptolemaic solar system to be who didn’t find the Ptolemaic solar system to be

satisfactory from a philosophical view due to the large satisfactory from a philosophical view due to the large

number of epicycles. Copernicus proposes a number of epicycles. Copernicus proposes a

heliocentric system of the universe with Earth being heliocentric system of the universe with Earth being

just another planet orbiting the sun in uniform circular just another planet orbiting the sun in uniform circular

motion (circle at constant speed). motion (circle at constant speed).

CopernicusCopernicusCopernicus reserved publication of his book, Copernicus reserved publication of his book, On the On the

Revolutions of the Heavenly SpheresRevolutions of the Heavenly Spheres, till he was near , till he was near

death to avoid confrontation with the church which was death to avoid confrontation with the church which was

dominated by Aristotelian thinkers. His work and its dominated by Aristotelian thinkers. His work and its

consequences gave a new political meaning for the consequences gave a new political meaning for the

word revolution.word revolution.

Note: Most people were illiterate. The exception was Note: Most people were illiterate. The exception was

the wealthy and the clergy since they ran the the wealthy and the clergy since they ran the

government and studied scriptures. They were wellgovernment and studied scriptures. They were well

educated in all subjects including Aristotelian educated in all subjects including Aristotelian

Mechanics.Mechanics.

CopernicusCopernicusIn his book, Copernicus also included a discussion of In his book, Copernicus also included a discussion of

epicycles and other platonic ideas. Thus, his radical epicycles and other platonic ideas. Thus, his radical

ideas were almost lost. However, the heliocentric solar ideas were almost lost. However, the heliocentric solar

system did have a powerful effect on Galileo and system did have a powerful effect on Galileo and

Kepler. There is also some arguments supporting that Kepler. There is also some arguments supporting that

other famous people of this time became Copernicans other famous people of this time became Copernicans

including Dante and Shakespeare. including Dante and Shakespeare.

Testing ModelsTesting ModelsWhat evidence supported the Copernican model of the What evidence supported the Copernican model of the

solar system?solar system?

Answer: None at this timeAnswer: None at this time

Galileo was a devoted Copernican and would begin Galileo was a devoted Copernican and would begin

collecting data that led to the downfall of the Ptolemaic collecting data that led to the downfall of the Ptolemaic

solar system. However, when the church offered to solar system. However, when the church offered to

rule in his favor if he could prove that the Earth moved, rule in his favor if he could prove that the Earth moved,

he had no proof.he had no proof.

AstrologyAstrologyPeople of the 1500’s were strong believers in witch People of the 1500’s were strong believers in witch

craft and in astrology. The ruling class believed that craft and in astrology. The ruling class believed that

their actions were ruled by the stars. Most their actions were ruled by the stars. Most

academicians including Kepler made a living by academicians including Kepler made a living by

casting Royal horoscopes. casting Royal horoscopes.

Conjunction is an astronomical event in which planets Conjunction is an astronomical event in which planets

are aligned. During the 1500’s, the minor planets were are aligned. During the 1500’s, the minor planets were

predicted to align (looks like a very bright star). predicted to align (looks like a very bright star).

However, the Ptolemaic tables were off a few days However, the Ptolemaic tables were off a few days

and the Copernican tables were worse.and the Copernican tables were worse.

Tycho BraheTycho BraheA Danish noble who realized that the reason the A Danish noble who realized that the reason the

astronomical tables incorrectly predicted the date of astronomical tables incorrectly predicted the date of

the conjunction was that no one had made the the conjunction was that no one had made the

necessary precise measurements of the stars.necessary precise measurements of the stars.

Brahe built the best astronomical observatory and Brahe built the best astronomical observatory and

instruments of the time. His measurements of the instruments of the time. His measurements of the

locations of the stars were 5 times more precise than locations of the stars were 5 times more precise than

previous measurements. previous measurements.

Tycho BraheTycho BraheBrahe was not a nice man. He especially didn’t like the Brahe was not a nice man. He especially didn’t like the

serious Johannes Kepler who he toyed with.serious Johannes Kepler who he toyed with.

Brahe had a silver nose because his nose had been Brahe had a silver nose because his nose had been

cut-off during a sword fight.cut-off during a sword fight.

On his death bed, Brahe begged Kepler to analyze his On his death bed, Brahe begged Kepler to analyze his

data and to publish Brahe’s model of the solar system. data and to publish Brahe’s model of the solar system.

However, Brahe’s family kept the data since they However, Brahe’s family kept the data since they

thought it might be worth money so Kepler broke in thought it might be worth money so Kepler broke in

and stole the data.and stole the data.

Tychonic UniverseTychonic UniverseIn the Tychonic Universe, the Sun orbits the Earth, but In the Tychonic Universe, the Sun orbits the Earth, but

all other planets orbit the Sun. This model is important all other planets orbit the Sun. This model is important

because it eliminated the concept of the crystal because it eliminated the concept of the crystal

spheres and freed astronomers from the concept that spheres and freed astronomers from the concept that

all motion had to be circular.all motion had to be circular.

Tycho’s most important contribution was his precise Tycho’s most important contribution was his precise

measurements since the new measurements showed measurements since the new measurements showed

that Mar’s orbit could not be explained using a circle. that Mar’s orbit could not be explained using a circle.

Johannes Kepler (1571-1630)Johannes Kepler (1571-1630)Kepler was one of the great geniuses of all time. He Kepler was one of the great geniuses of all time. He

developed the laws of planetary motion and almost developed the laws of planetary motion and almost

developed the Calculus.developed the Calculus.

Kepler had a rough life:Kepler had a rough life:

1.1. Father deserted familyFather deserted family

2.2. Raised in OrphanageRaised in Orphanage

3.3. Rough MarriagesRough Marriages

4.4. Religious PersecutionReligious Persecution

5.5. Mother tried as a witchMother tried as a witch

6.6. Children were unsuccessfulChildren were unsuccessful

Johannes KeplerJohannes KeplerKepler began wandering Europe on January 1, 1600. Kepler began wandering Europe on January 1, 1600.

He eventually went to see Brahe where he spent He eventually went to see Brahe where he spent

eighteen months working for Brahe and trying to get eighteen months working for Brahe and trying to get

Brahe to show him his measurements.Brahe to show him his measurements.

Once he has Brahe’s data, he spends sixteen years Once he has Brahe’s data, he spends sixteen years

analyzing data before he finds that three statements analyzing data before he finds that three statements

can describe all of the motions in the heavens can describe all of the motions in the heavens

(Kepler’s Laws of Planetary Motion).(Kepler’s Laws of Planetary Motion).

Kepler’s 1Kepler’s 1stst Law Law

All planets travel in ellipses with the Sun at one foci.All planets travel in ellipses with the Sun at one foci.

This discovery is forced upon Kepler by the This discovery is forced upon Kepler by the

eccentricity of the orbit of Mars which are shown in eccentricity of the orbit of Mars which are shown in

Brahe’s data!!Brahe’s data!!

x

This drawing is exaggerated for the 5 major planets with Mars being the most eccentric at only 8% away from a circle.

Kepler’s 2nd LawKepler’s 2nd Law

All planets trace out equal area in equal time.All planets trace out equal area in equal time.

This will later be found to be a consequence of This will later be found to be a consequence of

conservation of angular momentum.conservation of angular momentum.

x

When a planet is far from the sun it moves slower such that the area traced out is the same for the same amount of time.

Kepler’s 3nd LawKepler’s 3nd Law

The period (time required to complete a revolution – The period (time required to complete a revolution –

i.e. the year) for a planet squared is proportional to the i.e. the year) for a planet squared is proportional to the

cube of the radius of its semi-major axis.cube of the radius of its semi-major axis.

x a

32 akT

Kepler’s LawsKepler’s LawsKepler’s laws were incredibly powerful in that they Kepler’s laws were incredibly powerful in that they

explained all know observations with just three ideas. explained all know observations with just three ideas.

They also gave support to the Copernican model of They also gave support to the Copernican model of

the solar system. the solar system.

Kepler couldn’t explain why his laws were true!! Kepler couldn’t explain why his laws were true!!

He simply knew that they fit the data. It will take Isaac He simply knew that they fit the data. It will take Isaac

Newton to provide the synthesis that Aristotle had Newton to provide the synthesis that Aristotle had

done previously.done previously.