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Keys to Success in PHY 111
 Show up on time and stay
 Do the assignments and extra credits
 Take notes and review them
 Take advantage of resources
 Pay attention
 Practice, work the problems
 Learn the required math and analysis
 Don’t annoy the Instructor
When you have completed Chapter 1 you should be able
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1. Outline the scientific method.
2. Explain why the scientific method has been more successful than other approaches to
understanding the universe.
3. Distinguish between a law and a theory.
4. Discuss the role of a model in formulating a scientific theory.
5. Give the reason why Polaris remains most nearly stationary in the sky.
6. Define constellation.
7. Tell how to distinguish planets from stars by observations of the night sky made several
weeks or months apart.
8. Compare how the ptolemaic and copernican systems account for the observed motions of
the sun, moon, planets, and stars across the sky.
9. Explain the significance of Kepler's laws.
10. State why the copernican system is considered correct.
11. Define day and year.
12. Define fundamental force.
13. Explain why the earth is round but not a perfect sphere.
14. Explain the origin of tides.
15. Explain in terms of the scientific method why the discovery of Neptune was so important
in confirming the law of gravity.
16. Change the units in which a quantity is expressed from those of one system of units to
those of another system.
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17. Use metric prefixes for small and large numbers.
18. Use significant figures correctly in a calculation.
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The Scientific Method
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Formulating a problem
Observation and experiment
Interpreting the data
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initially, a scientific interpretation is usually called a hypothesis
may lead to a rule or law to which data seems to conform
may be a theory, which is a more ambitious attempt to account for
what has been found
Testing the interpretation by further observations
and experiments
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This allows to see whether the interpretation correctly predicts the
results
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The Scientific Method
tam1s5_1
Figure 1-1
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Key aspects of Scientific Method
 Science looks for consistency of its LAWS and Theories
 Any findings that contradict known laws set off serious investigations
 Observations
 Experiments
 Data
 Measurements, accuracy validation, repeatability of results
 Peer reviews and validations by scientific community, publication in
scientific journals, papers at conferences
 Science does not readily accept a hypothesis that cannot be
DISPROVED ( there must be a way to validate )
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Laws Of Nature
 Everything in the universe behaves in a certain, regular way.
 These behaviors are known as the laws of nature.
 To be a law of nature, a certain regularity must hold true
everywhere at all times within its range of applicability
 Laws are predict behavior of physical phenomena
 We use these laws to predict phenomena not yet discovered
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Uranus’ irregular motion led to discovery of Neptune
 The laws of nature can suggestwhat is going on in places we cannot
examine directly
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Sun’s interior and interior of an atom
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Theories and Laws
 Law tells us “what” happens
 Theory tells us “why” it works as it does
 Scientific Theory is the strongest and deepest
understanding
( unlike the popular concept that theory is a wishy
washy idea )
 Einstein’s general theory of relativity interprets gravity
as a distortion of space-time around a body of matter
 This theory modifies Newton’s law of gravity and shows
that light should be affected by gravity
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Why Science is Successful
 Science is a powerful tool for investigating nature
because of the constant testing and retesting of its
findings
 Laws and theories are not necessarily the final word;
they are only valid as long as no contrary evidence
comes to light
 Discrepancies must be larger than measurement
errors
 Laws may be found to operate with in certain
boundaries and become less accurate outside those
boundaries
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What is Cosmology?
 Cosmology is the study of the Universe as a whole
 What is the extent of the universe
 How old is the universe
 What does universe consist of
 How is the matter and energy distributed through out
 Is the Universe expanding, static or contracting
 What is the fate of the universe
 How are galaxies formed
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Andromeda Galaxy
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The Solar System
 A survey of the sky
 Polaris (the North Star)
 this star seems barely to move in the northern sky because it happens to lie
almost directly over the north pole in line the the earth’s axis
 Constellations
 Easily recognizable groups of stars, such as the Big Dipper in Ursa Major
 The Zodiac constellations are in or near the plane of the Equator
 Planets visible to the naked eye include:
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Mercury
Venus
Mars
Jupiter
Saturn
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Constellation Orion
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Orion
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Orion Nebula
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The Solar System
 The Ptolemaic System
 Ptolemy A.D. 100-170
 The Earth as the center of the universe
 Earth stands at the center of the universe, motionless,
with everything around it moving about it in circles or in
combinations of circles
 Stars are inside the solar system
 His system included 80 epicycles and was supreme until
Copernicus in 1543
 He named 48 of today’s 88 constellations
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The Ptolemaic System
Figure 1-7
tam1s5_5
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The retrograde motion of Mars as shown
in a series of images taken on the same
photographic plate.
Ptolemy explained this motion using a geocentric (Earthcentered) model of the solar system in which the planets
orbited the Earth indirectly by moving on epicycles which in
turn orbited the earth. Go to publishers web site to see
Animation
Nicolaus Copernicus (1473–1543)
Copernicus, the youngest of four
children, was born in Torun, Poland.
He pursued his higher education in
Italy, where he received a doctorate
in canon law and studied medicine.
Copernicus developed a
heliocentric theory of the known
universe and just before his death in
1543 published this work under the
title De Revolutionibus Orbium
Coelestium. His revolutionary theory
was flawed in that he assumed that
the planets had circular orbits
around the Sun. His model still
needed epicircles.This was
corrected by Johannes Kepler.
The Solar System
 The Copernican System
 Nicolaus Copernicus (1473-1543)
 Developed the idea that the earth and all the other
known planets rotated around the sun in a circular
orbit
 Earth rotates daily on its axis
 Moon revolves about Earth
 Stars are far away (Parallax still not measureable )
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The Copernican System
tam1s5_6
Figure 1-8
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The Solar System
 Kepler’s Laws – how the planets actually move
 Using Tycho Brahe’s extensive data which was appropriated by Kepler
upon his death in 1601, Kepler hoped to prove Copernicus correct once
and for all
 He discarded current theories on the solar system and began to look for
a new cosmic design that would fit Tycho’s observations better.
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Johannes Kepler 1571 to 1630
 Kepler used Tycho Brahe’s Mars data
 Accuracy was best of the time ( 2 arc min)
 He struggled for 4 years looking for fit
 Tried to fit all manner of shapes
 He came up with the largest egg in history
 Unwilling to compromise over small errors
 Discovered finally Mars moved in elliptical path
 He went on to publish his three laws of planetary motion
Kepler’s 3 Laws of Planetary Motion
 Kepler’s First Law:
 The paths of the planets around the sun are ellipses, not
circles, with the sun at one focus
 Kepler’s Second Law
 A planet moves so that its radius vector sweeps out equal areas
in equal times
 Kepler’s Third Law:
 The ratio between the square of the time needed by a planet to
make a revolution around the sun and the cube of its average
distance from the sun is the same for all the planets
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An ellipse can be drawn with a pencil, a loop of string, and two
thumbtacks, as shown. If the string is kept taut, the pencil traces out an
ellipse. The two thumbtacks are located at the two foci of the ellipse.
The amount of elongation in a planet’s orbit is defined as
its orbital eccentricity. An orbital eccentricity of 0 is a
perfect circle while an eccentricity close to 1.0 is nearly a
straight line. In an elliptical orbit, the distance from a planet
to the Sun varies. The point in a planet’s orbit closest to
the Sun is called perihelion and the point in a planet’s orbit
farthest from the Sun is called aphelion.
Kepler’s First Law: The orbit of a planet about the Sun is
an ellipse with the Sun at one focus.
Kepler’s Second Law: A line joining the planet and the
sun sweeps out equal areas in equal intervals of time.
Kepler’s Third Law
(Period of a Planet) 2
 same for all planets
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(Average Orbit Radius)
2
T
 same for all planets
3
R
 T=Period of the planet which is the time it takes for a planet to
orbit the sun
 R= Average radius of the planets orbit
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A Demonstration of Kepler’s Third Law
Why Copernicus was Right
 Copernican Heliocentric model is hugely more appropriate
because there is direct evidence for motions of the planets
around the sun and for the rotation of the Earth
 Evidence includes the change in apparent position of nearby stars
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relative to the background of distant ones as the Earth revolves
around the Sun (Parallax)
Shifts are small because stars are far away, but they have been found
Inner planets show phases like the moon
The low frequency of Solar Eclipses ( If Sun circled Earth, they
would occur more frequently )
Tides are manifestation of earth rotation
The Earths equatorial bulge indicates rotation
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In 1610, Galileo discovered
four “stars” that move back
and forth across Jupiter. He
concluded that they are four
moons that orbit Jupiter just
as our Moon orbits Earth.
These observations made
by Jesuits in 1620 of Jupiter
and its four visible moons.
Universal Gravitation
 A force of some kind was holding planets in their orbits
around the sun
 Three centuries ago, Isaac Newton (1642-1727) had the
idea that the force holding planets in orbit was the same
force that pulls things to the Earth’s surface
 This is known as the Law of Gravity
 Discovery supported the Copernican model of the solar system
 And accounts for Kepler’s Laws
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What is Gravity?
 Gravity is a fundamental force*
 A force that can’t be explained in terms of any other
force
 Only four fundamental forces are known:
 Gravity
 Electromagnetic
 Weak
 Strong
* Einstein’s Theory of General Relativity does not consider
gravity to be a force
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Four Fundamental Forces
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Gravity
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Gravitational forces act between all bodies everywhere
and hold together planets, stars, and galaxies
Rel strength 10-37
Electromagnetic
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electromagnetic forces act between electrically
charged particles and govern the structures and
behavior of atoms, molecules, solids, and liquids
Electromagnetic forces can act at unlimited distances
Rel strength 0.007
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Four Fundamental Forces
 Weak and Strong
 The weak and strong forces have very short
ranges and act inside atomic nuclei
 Rel strength of strong =1 (accounts for holding
nucleus together)
 Rel strength of weak = 1 x 10-6
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Accounts for beta decay, isotopes, nuclear fusion
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The Gravitational Pull of the Earth on the Moon
tam1s5_12
Figure 1-15
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What is Gravity?
 The Earth is round because gravity squeezes it to this
shape
 However, the earth is not a perfect sphere, which was
apparent to Newton
 Newton stated that since the earth is spinning , inertia
causes the equatorial portion to bulge
 As a result the earth and is also slightly flatter at the
poles
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Gravity Forces the Earth to be Round
tam1s5_19
Figure 1-17
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Gravity and Tides
Spring Tide
Neap Tide
Syzygy configuration
In fact, the tidal bulge lags the earths rotation slightly
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The Origin of the Tides
d
Figure 1-19
tam1s5_21
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What is Gravity?
 The discovery of Neptune
 In Newton’s time, only 6 planets were known:
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Mercury, Venus, Earth, Mars, Jupiter, and Saturn
In 1781, Uranus was discovered
 Little by little Uranus moved away from its predicted
path among the stars
 Uranus was moving from its predicted path because of
the planet Neptune
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Planet Uranus
 Discovered by William Herschel
 Rotational period (hours)-17.9
 Date of discovery 1781
 Orbital period (years) 84.01
 Mass (kg)8.686e+25
 Mean orbital velocity (km/sec)
 Mass (Earth = 1)1.4535e+01
 Equatorial radius (km)25,559
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 Equatorial radius 4.01(Earth = 1)
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 Mean density (gm/cm^3)1.29
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 Mean distance from the Sun
(km)2,870,990,000
 Mean distance from the Sun
 (Earth = 1)19.1914
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6.81
Orbital eccentricity 0.0461
Tilt of axis (degrees)97.86
Orbital inclination
(degrees)0.774
Atmospheric composition
Hydrogen 83%
Helium 15%
Methane 2%
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Discovery of Neptune
http://history-world.org/neptune,%20Discover%20of.htm
 As early as 1821, astronomers were noting
discrepancies in the orbit of Uranus
 Galle wrote to Leverrier on 25
September, 1846 saying:-
 On 3 July 1841 Adams, while still an
undergraduate at Cambridge, wrote
 Monsieur, the planet of which you
Formed a design in the beginning of this
week, of investigating, as soon as possible
after taking my degree, the irregularities
of the motion of Uranus, which are yet
unaccounted for
 On 31 August, 1846 LeVerrier published
his third paper on the "new planet". This
time he gave full details of the predicted
orbit and the mass. He also deduced the
angular diameter and wrote to Galle: It should be possible to see the new planet
in good telescopes and also to distinguish
it by the size of its disk.
indicated the position really exists.
 Leverrier replied: I thank you for the alacrity with
which you applied my instructions.
We are thereby, thanks to you,
definitely in possession of a new
world.
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How Many of What?
 Standard quantities such as the mile are known as
units
 Every measurement has a number that
answers “how many”
 And a unit that answers “of what”
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The SI System
 International system of units
 Derived from the old metric system
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Meter (length), kilogram (mass), joule (energy), second
(time), watt (power)
 Advantage is their subdivisions and multiples are in
steps of 10, 100, 1000, etc
 See Table 1-1 for subdivisions and multiples of SI Units
 See Table 1-2 for conversion factors for length
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In Class Review
1. Which statement best characterizes the nature of science?
a. The laws and theories of science are based on belief
and speculation.
b. Science is a living body of knowledge, not a set of
unchanging ideas.
c. Science has done a poor job of explaining physical
phenomena and has failed to
improve the quality of human life.
d. Science is superior to other aspects of human culture
such as religion, art, and music.
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2. A scientific law
a. is seldom based upon experimental evidence
since it can never be considered to be
absolutely true
b. usually states a regularity or relationship that
describes how nature behaves in a certain,
specific way
c. explains why certain phenomena in nature take
place
d. is known to be true beyond a shadow of a doubt
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3. The ptolemaic system fulfilled the requirements
of a scientific theory because
a. its explanations of celestial motions, based on
observations, resulted in testable predictions
b. it was presented openly for public inspection
when included in Ptolemy's Almagest
c. it was believed to represent an accurate view of
the universe and solar system by
religious leaders and learned scholars of the time
d. it provided a "common sense" explanation
concerning the observed motions of
heavenly bodies
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4. The principle known as Occam’s razor states that
a. the most complicated scientific explanation for a given
phenomenon is likely to be correct
b. a scientific hypothesis that makes common sense is most
likely to be correct
c. scientific inquiry can never lead to a complete
understanding of the natural world
because it is impossible to precisely measure any physical
parameter
d. the simplest scientific explanation for a phenomenon is
most likely to be correct
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6. The time it takes a planet to make one complete trip
around the sun is called the planet's
a. revolution
b. orbit
c. rotation
d. period
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7. The modern version of the Copernican system is
considered to be correct because
a. most people believe that the copernican system is
correct, and the majority viewpoint
rules
b. predictions of planetary motions based on the
Copernican system proved to be correct
c. there is direct evidence that the earth rotates and the
planets revolve around the sun
d. a committee of scientists has certified that the
Copernican system is correct
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8. When observable evidence does not agree with a
scientific theory
a. the truthfulness of the evidence must be questioned
since a theory is never wrong
b. the evidence is ignored and the theory remains valid
c. the theory is reduced in status to a hypothesis
d. the theory must be modified or discarded
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9. Spring tides
a. occur only in the spring
b. occur when the sun and moon are in
line with the earth
c. have a low range between high and low
water
d. occur when the sun and moon are 90°
apart relative to the earth
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10. The points corresponding to the
positions of the tacks are called
a. epicycles
b. foci
c. planets
d. Orbits
11. The sun would occupy a position
a. at either point F1 or F2
b. at the center of the ellipse
c. at the pencil
d. somewhere on the circumference of the
ellipse
12. The drawing is a visual representation
of
a. Newton's law of gravity
b. Kepler's first law of planetary motion
c. Kepler's second law of planetary motion
d. Kepler's third law of planetary motion
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13. The shaded areas are:
a. Equal only for MARS
b. Represent Kepler’s 3rd law
c. Are equal area only if time AB is same as
time BC
d. The equal area rule only applies at aphelion
and perihelion so the shaded areas mean
nothing
14. The planet would be traveling the fastest along that
portion of its orbit represented by the
distance between the letters
a. a and b
b. c and d
d. none of the answers is correct because the planet's speed
remains constant along its orbit
15. If the average orbit radius of the planet is increased, the
period of the planet will
a. decrease
b. increase
c. remain unchanged
d. decrease or increase depending on the mass of the planet
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