Aristotle (384-322 B.C)

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Aristotle(384-322 B.C)

• Greek philosopher, scientist, and educator.
• Systematized existing knowledge
• Made observations
• Collected specimens
• Gathered together, summarized, and classified
  existing knowledge of the physical world

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Aristotle(384-322 B.C)

• Believed the Earth was a sphere because
• The Earths shadow on the Moon during a lunar
  eclipse is always round.

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Aristotle(384-322 B.C)
Aristotle(384-322 B.C)

• Believed the Earth as sphere because
• Stars near the celestial pole are higher in the
  sky the farther north you travel.

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Aristotle(384-322 B.C)

• Believed the Earth was a sphere because The fact
  that objects fall to Earth towards its center
  means that if it were constructed of small bits
  of matter originally, these parts would naturally
  settle into a spherical shape by compression

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Ships Sailing Over the Horizon
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Aristotle on Motions
Violent Motion
Natural Motion
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Natural Motion

• Is caused by objects striving to get to their
  proper place.
• The proper place is determined by how much of
  each of the fours elements (Earth, water, air,
  fire) the object contains.

Smoke (made of Air) strives to get to the Air.
A feather (part Earth, part Air) strives to get
to the Earth, but is slowed by also striving to
get to the Air.
A rock (made of Earth) strives to get to the
Earth.
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Violent Motion
Once in flight, air filling in behind and pushing
on the arrow keeps it going

• Results from something external pulling or
  pushing on an object in opposition to its natural
  motion
• Requires a constant push or pull to sustain the
  motion

Lifting the rock opposes the rocks striving to
the Earth.
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Some Aristotelian Conclusions

• A heavier object (having more earth) will fall to
  the ground faster than a light object.
• If you stop pushing an object, it will stop
  moving.

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Aristotles Universe

• The Earth is stationary and at the center.
• The heavens are 55 concentric crystalline sphere,
  each carrying celestial objects and rotating.
• Celestial bodies are perfect spheres made of a
  perfect and unchanging substance (quintessence).
• A Prime Mover keeps the heavens in motion.

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Eratosthenes(276-195 BC)
At noon on the Summer Solstice, sunlight
struckthe bottom of a vertical well in Syene,
Egypt.

• At that moment, the shadow cast by a vertical
  obelisk in Alexandria (5,000 stadia distant)
  showed that the Sun was 7.2 degrees away from the
  vertical.

Therefore, the Earths circumference is5000 x
(360/7.2) 250,000 stadia
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How Accurate Was Eratosthenes?

• Historians disagree on how big a Greek stadium
  was.
• Depending on what the correct conversion to the
  modern units is, Eratostheness estimate was
  between 1 and 20 percent larger than the modern
  value.

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Why Does It Matter?

• The panel of experts appointed by King
  Ferdinand to review Columbuss proposal to sail
  to India was aware of Eratostheness work.
  Because of this, they ruled that the distance was
  too great and that he therefore should not go.

Columbus, using either error-laden estimates of
others, or using an incorrect conversion factor,
believed that the distance was only 1/3 or ½ of
the true distance.Queen Isabella overruled the
experts and sided with Columbus.
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Beginnings of modern, empirical science Ibn
al-Haythem (965-1040 CE)

• Born in Basra, Iraq
• Educated in Basra and Baghdad
• Worked in Egypt and Spain
• Developed the modern theory of optics by taking
  careful measurements in repeatable experiments
• Considered various theories of light and designed
  and carried out experiments to determine which
  theory might be more accurate

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Ibn al-Haythem

• Studied the propagation of light and the nature
  of colors
• Studied optic illusions and reflections
• Studied the refraction (bending) of light rays
  when pass from one transparent medium to another
  (air, water) and studied the angle of incidence
  and refraction quantitatively
• Dispersion of light into colors
• Studied the way the light travels through the
  atmosphere and estimated the thickness of the
  atmosphere

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Beginnings of modern, empirical science Roger
Bacon (1214-1294 CE)

• Born in England, worked in Paris and Oxford
• Became a Franciscan friar
• Vigorously encouraged experimental science
• Asserted that the study of the natural world by
  observation and exact measurement was the surest
  foundation for truth.
• Having read al-Haythems works, he performed
  optical experiments with lenses and mirrors,
  described spectacles

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Roger Bacon

• The strongest arguments prove nothing so long as
  the conclusions are not verified by experience.
  Experimental science is the queen of sciences and
  the goal of all speculation.
• For the things of this world cannot be made
  known without a knowledge of mathematics
• All science requires mathematics. 

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Galileo Galilei(1564-1642)

• Defined new concepts in addition to discovering
  objects
• Simplified investigations through
• Reducing scope (focusing on one issue at a time)
• Idealization (thinking away complications)
• Designed experiments to test hypotheses
• Described the physical world with mathematics

Galileos approach sets the stage for all of
modern science.
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Galileo on authority, measurement, and math
In questions of science the authority of a
thousand is not worth the humble reasoning of a
single individual.
Count what is countable, measure what is
measurable, and what is not measurable, make
measurable.
Philosophy is written in this grand book, the
universe, which stands continually open to our
gaze. But the book cannot be understood unless
one first learns to comprehend the language and
read the letters in which it is composed. It is
written in the language of mathematics, and its
characters are triangles, circles, and other
geometric figures without which it is humanly
impossible to understand a single word of it
without these, one wanders about in a dark
labyrinth.
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Galileo on Falling Bodies

• Experiment drop objects of various weights from
  the Leaning Tower of Pisa
• Conclusion Except for small effects of air
  resistance, objects of various weights fall
  together and reach the ground at the same time.

Aristotle observed that there was always a
resistive medium in the world around him.
Galileo imagined what would happen if there was
no resistance.
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Galileo on Motion

• Experiment Observe motions of various objects
  going down inclined planes.
• Conclude In the absence of friction, a rolling
  ball rolling along a horizontal surface
• will neither speed up nor slow down
• will never come to rest.

Aristotle motion requires a push or a pull to
keep moving. Galileo with no interference, a
moving object will kepp moving in a straight line
forwever.
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Inertia

• Galileo defined a new word

Inertia the property of an object that tends to
keep it moving straight ahead or that resists
changes in it motion
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Galileos Universe

• Seeing that Jupiter hadmoons orbiting meantthat
  celestial bodies(such as our Moon)could orbit
  objects otherthan our Sun.
• Extending the idea of inertiato circular motion
  meant thatthe Earth could circle theSun
  indefinitely.
• So Galileo adopted the Copernican model of the
  universe

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• Mathematics is the language with which God has
  written the universe.
• Philosophy is written in this grand book - I
  mean the Universe - which stands continually open
  to our gaze, but it cannot be understood unless
  one first learns to comprehend the language and
  interpret the characters in which it is written.
  It is written in the language of mathematics, and
  its characters are triangles, circles and other
  geometrical figures, without which it is humanly
  impossible to understand a single word of it.
• Galileo