Physics 10 Lecture 2

Professor Smoot's Class

While there was some development of physics and astronomy in ancient Sumeria and Babalonia most scholars trace the beginnings of science to the Greeks.
The beginning of a long march toward more naturalistic science with an increasingly skeptical rationalism away from belief in the supernatural towards the natural.

A Brief Historical Time-Line

~2000 BC Migration of Greek-speaking Indo-Europeans into Aegean region.

The exploration of new lands and the development of sailing spurs the development of astronomical observations and mathematical interpretation.

1800 BC         Early Mesopotanian astronomical observations recorded
1700-1450 BC Minoan Civilization on Crete
                            Atlantis legend as volcano wipes out much of Greek civilization
1400 BC          Mycenean Civilization arises
1200 BC          Trojan War with Mycenaean Greeks
1100 BC          Dorian ascendency
900-700 BC    Homer's Iliad & Odyssey
776 BC           First Pan-Hellenic Olympic Games
600 BC           Thales of Miletus - birth of philosophy, first to predict a solar eclipse
580 BC           Sappho - flowering of Greek poetry
570 BC           Anaximander - develops a systematic cosmology
545 BC           Anaximeres - posits transmutation of underlying substance
525 BC           Pythagoras - begins development of his school
520 BC           Xenophanses - concept of human progress, philosophical monothesism
506 BC           Democratic reforms in Athens
                        Great rise of culture in Athens - Age of Pericles
450 BC           Emergence of Sophists
431-404 BC    Peloponnesian Wars
430 BC           Democratis - atomism
404 BC           Athens defeated by Sparta
399 BC           Trial of Socrates
387 BC           Plato founds Academy in Athens
367 BC           Aristotle begins 20 years of study at Plato's academy
368 BC           Aristotle tutors Alexander of Macedonia
                        Aristotle founds Lyceum in Athens
295 BC           Euclid's Elements
270 BC           Aristarchus proposes heliocentric theory
240 BC           Archimedes; develops classical mechanics and mathematics
146 BC           Greece conquered by Rome

Beginning the 6th century BC Thales, his successor, Anaximander, and Anaximeres began the process with systems and classification of nature.
Myths are replaced by development of a rational world order with underlying principles.

Parmenides - development of language and logic

Leucippus and Democritus put forth atomism - unchanging elements ceaselessly moving in the void (vacuum) at random.
Entirely material possessing neither divine order or purpose.

Pythagoras founds a school propounding the concept of numbers describing nature. Eventually, forced to exile in Italy.

Anaxagroras declared the Sun was not the god Helios but an incandescent stone larger than the Peloponnese and that the moon was composed of stone and received its light from the Sun.

All of these contribute to the march toward more naturalistic science away from the supernatural towards the rational.

A very major step/plateau was provided by Aristotle who wrote a series of books on all subjects.
He summarized the knowledge and theories of his predecessors presenting them in the best way and either accepted them
or argued against them and presented his replacement theories.
One of his books was in Latin entitled "Physics et Caelum", literally Physics and the Sky but a more modern title would be Physics and Astronomy as some of the effects he considered meteorology we know consider astronomy.

Physics and Cosmology of Aristotle

Counter arguments to predecessors models, particularly the atomists but many others
four plus one elements - fire, air, earth, water - and the fifth element, the quintesscense, perfect crystalline material
moment - circular motion in the heaven, straight motion on the earth. Motion in the heavens is continuous but on the Earth nothing moved without being pushed.
This leads to the idea that the circular motion of the stars is because they are on a large sphere which rotates once per 24 hours. And the planets and the moon are each on different nested spheres, eventually 8 nested spheres.
With centuries of astronomical observations in hand, Aristotle posed the problem of the planets - saving the phenomena as key to astronomy. The idea was to find a simple way to describe the motion of the planets (and stars) that could be used instead of long tables of observations. His predecessors, e.g. Thales of Miletus - birth of philosophy, first to predict a solar eclipse, clearly understood that the motion was regular and that the motion was nearly circular.
The end result for centuries was what we call the Ptolemaic model after Ptolemy who added epicycles. That is because the Greeks believed that the motion must be circular but the motions were not actually circular. By adding smaller spheres to the bigger spheres, one can approximate the observations more accurately - more epicycles makes for more accuracy.

How the Greeks put numbers to their cosmology

I think that many of you saw the lunar eclipse last night. The Greeks had observed many and noticed that the Earth's shadow was always round. The only object that always casts a round shadow is a sphere. Thus the Greeks realized that the Earth was spherical.

Eratosthenes' determination of the radius of the Earth. The cities were separated by about 500 miles and thus he could determine the earth had a radius of about 3,750 miles while today we estimate the mean radius of the Earth as 3,960 miles.

Aristarchus estimated the size of the moon to be about one quarter the size of the Earth or 940 miles in radius whereas the modern estimate is 1,080 miles. He also was able to determine the distance to the moon which he found to be 225,000 miles compared to the modern value of about 239,000 miles.

Galileo and Galilean Relativity

Science should be based upon observations and experiments
Motion is relative. Rest is no different than any other uniform motion.

Demonstration - independence of motion in orthogonal directions

The independence of motion in orthogonal directions. Car on horizontal track which shoots ball vertically. Ball comes back down into cart as long as it is in uniform motion.

Demonstration - Hunter and Monkey

Demonstrates that the rate of change of motion is independent of velocity. The projectile and the monkey drop down the same amount in the same time.