Ch 1: About Science and a Brief History of Physics
Q: What is science?
 the body of knowledge that describes the order within
nature and the causes of that order
 ongoing human activity representing collective efforts,
findings, wisdom
 dedication to gathering knowledge about the world,
organizing and condensing it into testable laws and
theories
 regulations of the world that allow for predictions about
the world
The History of Science
3rd – 4th centuries B.C., great scientific discoveries were
made in Greece, and quickly spread throughout the
Mediterranean world.
5th century A.D., scientific discoveries came to a crashing
halt with the fall of the Roman Empire.
Throngs of
Barbarians destroyed almost everything in their path as they
took over Europe, and caused the “dark ages” to fall upon the
people.
At this same time, the Chinese and the Polynesians
were charting stars and planets.
Arab nations were developing mathematics and
learning about the production of paper, glass, metals and
chemicals.
10th – 12th centuries, Greek science was re-introduced to
Europe that eventually entered Spain.
13th century, universities sprouted throughout Europe.
14th century, gunpowder was developed and changed
the power structure (socially and politically) throughout
Europe.
15th century, Leonardo daVinci beautifully blended art
and science.
16th century, Copernicus stated that Earth revolves
around the sun. This conflicted with the popular view that the
Earth was the center of the universe, and with the church’s
teachings at the time, and his findings were banned for almost
200 years. Morrover, he was almost executed for his findings!
Galileo Galilei was arrested for popularizing
Copernicus’ findings, and for his other contributions to science
at that time.
Q: Has this kind of extreme resistance to new knowledge ever
happened elsewhere in history?
Scientific Measurements
Q: Why do you need to take measurements in science?
Q; What is accuracy? Precision? Which of these, if any, do
“sig figs” address? Why are sig figs necessary?
Internet assignment: Be prepared to discuss this
tomorrow during class.
Web Assignment: How did Eratosthenes discover the size of
the Earth in 235ish B.C.?
Aristarchus and the Size of the Moon
Aristarchus, a Greek astronomer and mathematician from
“back in the day,” 310 – 230 B.C., used geometry to accurately
determine both the moon’s diameter and its distance from the Earth.
Though he relayed his findings in 240-ish B.C., they were not confirmed
until a short 17 centuries later!!!
Holy
, how impressive!!
How’d he do it?
He compared the size of the moon to that of the Earth by watching a
lunar eclipse (eclipse of the moon).
 When the Earth is exposed to sunlight, it casts a shadow.
 When the moon passes into this shadow, you get a lunar eclipse.
Using geometry, Aristarchus figured out that the Earth’s shadow was
2.5 moon diameters. Because of the fact that the sun is sooooooo huge,
the shadow from the Earth tapers, because the sun’s rays taper with
distance, as you can really see during a solar eclipse.
In fact, during a solar eclipse, the amount of taper is a “whole moon
diameter” from the moon to the Earth. So, Aristarchus reasoned the
Earth’s shadow will taper the same amount in the same distance. Thus,
the Earth’s diameter must be 1 + 2.5, or 3.5 times that of the moon. In
this way, Aristarchus determined the moon’s diameter to be 1/3.5 that
of the Earth. The presently accepted value of the moon’s diameter is
3640 km, which is within 5% of the value calculated by Aristarchus.
(He must have eaten his Wheaties!!)
Distance to the Moon and Sun
If you tape a dime to a window and view it with one eye so that
it blocks out the moon, you will find that your eye is about 110
coin diameters away. This coin diameter:coin distance is about
1:110, or 1/110. Using similar triangles, this is then the moon
diameter: moon distance ratio. So, the distance to the moon is
about 110 times its diameter. Since Aristarchus already
determined the moon’s diameter, this enabled the early Greeks
to determine the distance to the moon.
Using similar geometric logic (dime blocking view of the sun),
the sun diameter: sun distance ratio is also 1:110. Both the
moon’s and the sun’s images taper at the same angle (about
50). The problem was that one of those values had to be known
to determine the other for the sun’s measurements.
Aristarchus instead watched for the ½ full phase of the moon
with the sun still visible in the sky. At this point, then, the
sunlight must be falling on the moon at right angles to his line
of sight. This meant that the lines between the Earth and
moon, Earth and sun, and sun and moon form a right triangle.
If you know the angles of a right triangle and one of the sides,
you can calculate the length of any other side! Using this right
triangle geometry, Aristarchus determined the distance to the
sun to be about 20 times that of the moon. This estimate was
later determined to be far off. It is actually 400 times that of
the moon. His error was related to the fact that he errantly
determined the missing angle of the triangle to be 870 when it
was actually 89.80. Today we know that the sun is an average
of 150,000,000 km away. Since we know that, can we now
estimate the size of the sun? Yep, that’s your job!!
Size of the Sun
See CP3, p 2!
1.3 Scientific Method Usually credited with being the
principal founders of the scientific method are Galileo, Italian
physicist, and Francis Bacon, English philosopher. This
method allows for repeatability and is thus effective in gaining,
organizing and applying new knowledge. The steps, not
necessarily in this order, are:
1. Recognize a problem or solution
2. Formulate a hypothesis.
NOTE: It must be testable to qualify as a hypothesis!
3. Experiment many, many times
4. Formulate the simplest general rule that can be supported
by experimentation.
1.4 Scientific Attitude Just so you know, even a “fact” can
change with the acquisition of new information. We simply
accept something as fact, with appropriate empirical evidence,
unless and until it is disproved. If, in fact, something
previously accepted as fact (theory or law) has been proven to
be incorrect, it will be rejected, no matter the reputation of the
scientist(s) responsible for its previous discovery and
acceptance. Sometimes, though a specific theory or law has
been disproved, it still bears study, either because certain parts
still have merit, or because it still serves as an appropriate
scientific model.
1.5 Science, Art, and Religion
Science asks the question “how”, religion asks “why”, and the
arts allow for “expression” of ideas. Construct a Venn
diagram that might represent their interrelationship.
Try These: p 11-12
1. Which of these is / are (a) scientific hypothesis(es)?
a. Atoms are the smallest particles of matter that exist.
b. Space is permeated with an essence that is undetectable.
c. Albert Einstein was the greatest physicist of the 20th century
2. Two people get into an argument.
Person A only states one point of view, whereas person B
clearly states both his / her position, as well as the position of
person A. Who is more likely to be right?
1.6 Science and Technology
Science focuses on the gathering of information while
technology focuses on its application for practical purposes.
Obviously, they are intertwined.
1.7 Physics: The Basic Science
DEF: Physics = the study of the physical world. Obviously,
there are many areas of science and many subcategories and
areas of specialization therein. The life sciences include
biology, zoology, botany, and anatomy while the physical
sciences include geology, astronomy, chemistry and physics.
Physics is termed the basic science because it describes the very
nature of basic things like motion, forces, energy, matter, heat,
sound, light, waves, optics, and the inside structures of atoms.
Chemistry is about how matter is put together, how atoms
combine to form molecules, and how the molecules combine to
make up matter. Biology is even more complex, in that it
involves matter that is alive, alive, I say…
So, the diagram would look like this:
.
Biology
↓
Chemistry
↓
Physics
The concepts of physics reach up to, and impact, all of the
more complicated sciences. Thus, it is the basic science.
1.8 Keeping It In Perspective
Back in the day, centuries ago, the most talented artists,
architects, and artisans directed their genius to the
construction of the great cathedrals, temples, synagogues and
mosques. Many took centuries to build, so no one person was
able to witness both the beginning and end of construction.
This human energy was focused on constructing “spaceships of
faith” with the direction pointing toward the cosmos in some
fashion. Today, the focus of our most talented scientists,
engineers, and even artists and artisans are focused on
constructing actual spaceships that actually orbit throughout
space.
“The Earth is our cradle and has served us
well. But cradles, however comfortable,
are one day outgrown. So with the
inspiration that in many ways is similar
to the inspiration of those who built the
early cathedrals, temples, synagogues and
mosques, we aim for the cosmos. We live
in an exciting time!” (Paul Hewitt, 2002)