THE WAY OF SCIENCE

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CHAPTER 1

• THE WAY OF SCIENCE

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SUMMARY

• Stardust An Invitation to Science
• Observing the Night Sky
• Ancient Greek Theories An Earth-Centered
  Universe
• Copernicuss Theory A Sun-Centered Universe
• Keplers Theory A Sun-Focused Universe

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• 1.1 AN INVITATION TO SCIENCE
• Science Observing and understanding the natural
  world
• Reasons for learning science
• expanded awareness of the universe
• problems of modern society and their solutions
• understanding everyday technology
• Physics The study of universal phenomena

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• What is Physics?

"Physics" could best be described as the study of
(a) matter. (b) atoms in motion. (c) the
absolute, or certain, truths about the natural
world. (d) the general principles underlying
natural phenomena. (e) the application of
science to the needs of human beings.
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• 1.2 OBSERVING THE NIGHT SKY
• How does science operate
• Observe phenomena in nature
• Hypothesize on why they behave the way they do
• Test the hypothesis to se if it works
• If the hypothesis works, it is promoted to theory
• A theory should predict phenomena that have not
  been observed yet
• Astronomy Study of stars and other objects in
  space
• In this chapter, we will look at how various
  theories on astronomy evolved with time.

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• 1.3 ANCIENT GREEK THEORIES
• Babylonians and Egyptians (3000 BC) Knew about
  starts, sun, moon, and 5 planets
• Greeks (500BC) Sought to understand their motion
• Each sphere rotates at a uniform rate around
  Earth, roughly once a day.
• Pythagoras Pythagoreans formed a cult that
  believed in the importance of abstract ideas ?
  Mathematics

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• They were persecuted
• Deep influence on Plato and Aristotle
• Aristotle (200 years later) Earth is spherical
• Ships sink little by little below the horizon
• In Northern lands, noontime sun is lower in the
  sky
• Shadow cast by Earth on the moon, observed during
  eclipse, is spherical

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• Careful observations show that Mars generally
  moves from East to West at a variable rate and
  occasionally changes direction ? Retrograde motion

• Aristarchus theory Sun at Center of Universe ?
  dismissed because
• Earth is not the center of Heavens?
• Absurd that Earth moves.Too big Birds and
  clouds should be left behind

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• Epicycle theory Mars has a deferent and an
  epicycle (Fig. 10)
• Ptolemy Figs. 11 and 13
• He introduced 2 new ideas
• Earth is displaced slightly from the center of
  the deferent
• The center of the epicycle moves with unchanging
  speed, as seen from the equant

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• Ptolemy checked his theory with many quantitative
  measurements
• Used long sighting rods with a scale to measure
  the angular position of a planet
• Measured angle between the horizontal and the
  direction of the planet.
• Ptolemys theory gave a good explanation that
  agreed with the measured quantities
• These devices were accurate to within 0.2 degrees
• However, telescopes were not invented yet!!!

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• 1.4 COPERNICUS THEORY
• Polish (1473-1543 AD)
• He revealed his theory on his deathbed
• He looked at Earth as an object similar to
  other objects in space
• Like Pythagoras, he believed that motions were
  both circular and uniform (epicycle theory too
  complex)
• A sun-centered universe

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• The figure below shows the position of Earth and
  Mars at 9 different times. Mars is in retrograde
  motion during
• Times 4 to 6
• Times 3 to 5
• Times 1 to 5
• Times 4 to 7
• None of the time

Figure 1.16
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• Questions that Copernicus could not answered at
  that time
• How can Earth move?
• Why does it keep moving?
• Why arent birds, clouds and other objects left
  behind?
• He asked the same Questions regarding Ptolemys
  theory
• His findings led Newton to his work on gravity

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• 1.5 KEPLERS THEORY
• Brahe made a device that was so accurate that it
  is sometimes used today (0.04 degrees)
• After 20 years of observations, he found that
  neither Ptolemy nor Copernicus was right
• Kepler was Brahes disciple
• Each planet moves in a sun-focused ellipse An
  ellipse having the sun at one of its two focuses

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Keplers First Law The orbital paths of the
planets are elliptical (not circular) with the
Sun at one focus. What is an ellipse?
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In-class Problem (a) A circle can be defined as
the set of all points that are equidistant from
the center point, i.e., all the points are the
length of the radius away from the center . How
can one define an ellipse in terms of the lengths
of string indicated in the figure?
(b) The separation of the two foci determines the
ellipticity ( or the out of round) of the
ellipse. How can one make a circle out of an
ellipse by changing the positions of the foci?
A
B
HINT for (a) the string does not stretch.
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Perihelion and Aphelion of a planetary orbit
Perihelion point of closest approach. Aphelion
point at the greatest distance from the sun
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Keplers Second Law (addressing the speed of a
planet along its elliptical path) An imaginary
line connecting the Sun to any planet sweeps out
equal areas of the ellipse in equal intervals of
time.
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1.4 Copernicuss Theory A Sun-Centered Universe
Once Galileo had invented the telescope, he was
able to observe the phases of Venus. These phases
are totally incompatible with the Earth-centered
universe.
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• 1.6 DIALOGUE BETWEEN NATURE AND MIND
• Figure 1.25 shows the dynamic interplay between
  observations and theories

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When the last three planets were discovered
(Uranus, Neptune and Pluto), their orbits
followed closely Keplers theory
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• OBSERVATIONS Data-gathering
• MEASUREMENT Quantitative observation
• EXPERIMENT Observation designed and controlled
  by humans
• THEORY Confirmed framework of ideas that
  explains or unifies a group of observations
• MODEL Theory that can be visualized
• No scientific idea is ever certain.

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• There are two common misconceptions about
  scientific knowledge
• (a) Knowledge is absolute
• (b) Knowledge is dubious guesswork
• Knowledge is not absolute
• (a) Ptolemys and Copernicus theories were not
  absolute but they served their purpose.They
  predicted planetary motion to within 10
  arc-minutes
• (b) Keplers theory is not perfect
  either.planets severely deviate from their
  elliptical paths due to gravity between different
  planets.but is a good and useful
  approximation...

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• Science is not dubious guesswork
• (a) People who disliked Copernican theory on
  religious or other grounds argued that it was a
  mere theory.They did not use scientific facts
  to disprove it.
• (b) Imperfection of Earth meant that humankinds
  centrality to Gods plan was threatened. The
  catholic Church, for example, pronounced his
  theory as false, erroneous and heretical.
• (b) Only until 1992 that the Pope announced that
  the Church had wrongly accused Gallileo.
• (c) People that dislike the theory of evolution
  do the same.

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• Scientific Method The dynamic interplay between
  experience and thought
• Scientists generally believe in the Pythagorean
  ideal of a universe based on simple and elegant
  principles

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• 1.7 Copernican Revolution
• Roots of the scientific age
• Pythagorean belief in natural harmonies the
  universe is organized in a framework of
  principles that can be uncovered by observation
• Copernican revolution the Earth is a planet
  similar to the other planets, and the natural
  world is fundamentally the same everywhere

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Some of the things we know today

• Rejection of the geocentric illusion that Earth
  is at the center of the universe
• The sun is a star
• There are 400 billion visible aggregation of
  stars
• Each of the giant aggregation of stars is called
  a galaxy
• Ours is the Milky way

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Relative Sizes of the Sun and the planets
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An astronomical unit the average distance between
Earth and the Sun 149,600,000 km.
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A primary reason for you to learn science,
according to the textbook's opening section, is
(a) to pass on Western culture to the next
generation. (b) to increase your intelligence.
(c) to increase your awareness. (d) because a
broadly educated person can get a better job.
(e) Actually there is no good reason all this
scientific nonsense.
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Our primary reason for studying the theories of
Ptolemy, Copernicus, and Kepler was (a) to learn
some history of physics and astronomy. (b) to
learn about the methods and the validity of
science. (c) as a foundation for our later
study of Newtonian physics. (d) to see how
these early theories of atomic physics compare
with more recent studies. (e) so that we can
understand the structure of our solar system.
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The most significant difference between the
astronomical theories of Ptolemy and Copernicus
is (a) Ptolemy's is not based on scientific
evidence, while Copernicus's is. (b) Ptolemy
uses circular planetary orbits while Copernicus
uses elliptical orbits. (c) Ptolemy's theory is
sun-centered, whereas Copernicus's is
Earth-centered. (d) Ptolemy's theory is
Earth-centered, whereas Copernicus's is
sun-centered. (e) Ptolemy's theory does away
with many of the complexities of the Copernican
theory.
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The closest planet to the sun is (a) Pluto (b)
Earth (c) Jupiter (d) Mercury (e) Venus
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Which statement best describes the status of the
Copernican and Ptolemaic theories of the solar
system shortly after Copernicus invented his
theory about 1550, and before Tycho? (a)
Copernicus had proved that Ptolemy's theory was
incorrect. (b) Both theories agreed with the
experimental facts. (c) Ptolemy's theory fit
the experimental facts better than the Copernican
theory. (d) although Copernicus couldn't
disprove Ptolemy's theory, the Copernican theory
agreed much better with the experimental facts
than did the Ptolemaic theory. (e) both
theories were known to be wrong.
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Continuing the previous question, which of the
following statements best describes the status of
these two theories shortly after Tycho Brahe's
observations? (a) These observations showed
Ptolemy's theory to be the correct one. (b)
These observations showed Copernicus's theory to
be the correct one. (c) These observations
showed both theories to be correct. (d) These
observations showed both theories to be
incorrect. (e) These observations turned out to
have little or no bearing on either theory.