Section 7.33

The Road to Newton: The

Law of Universal Gravitation

Scientific Revolution: Copernicus to Galileo• Aristotelian Universe

• Geocentric• Planets revolve around

the Earth• Ptolemaic universe 200 A.D.

– Furthered Geocentric model

– Empyrean=home of the angels, immortal spirits

– Cosmos was a hierarchy of ascending perfection, heavens were purer than earth

Nicholas Copernicus• On the Revolutions of

Heavenly Orbs (1543)

• Heliocentric view

• Earth and planets revolve around the sun

• Used a mathematical construct to support

– was a little simpler than math used to explain Ptolemy's view

Brahe and Kepler• Tycho Brahe

– Studied the movement of planets: Mars

– Made vast amounts of detailed observations

Tycho Brahe's subterranean observatory on Ven, an island in the Sound between Denmark and Sweden.

• Kepler– Used the exact observations of

Brahe– Showed that Copernicus was

wrong about the perfect circular movements of planets around the sun

– Planets move in ellipses– Unified the mathematical harmony

of Copernicus and the stubborn facts of Tycho Brahe

• described the movement of the planets in explicit formulas which any competent person could verify

Kepler's model to explain the relative distances of the planets from the Sun in the Copernican System

Brahe and Kepler

Galileo (1564-1642)• Moon only reflects light and is made of

substances similar to Earth• observed its rough surface

• 1609 he built a telescope• saw spots on the sun as if the sun were

not pure planets have breadth stars do not

• Planets have satellites (Jupiter)• this verified Copernican theory• Declares that the Earth revolves around

the sun• Forced to recant his findings• Observed (from Leaning Tower of Pisa?)

that objects with different weight struck the ground at the same time

• Bodies in motion: inertia• change in motion rather than origination• dispensed with the need of an unmoved

mover

The Achievement of Newton: The Promise of Science• Why do planet not fly off in straight trajectories? • What force is involved?• Newton unified the work of Kepler and Galileo• Isaac Newton (1642-1727)

– Personally a secretive, petty, and vindictive man in daily conduct

– Drew on both Bacon and Cartesian traditions (believed that light was not mere subjective sensation but relied on math)

– Invented calculus and used a new measurement of the size of the earth

– Principia Mathematica (Mathematical principles of natural philosophy) 1687 or Principia

– Asks what kept the earth in motion and why do celestial bodies fall to the earth while the sun and moon do not?

– Kepler theorized that a force of mutual attraction existed b/t bodies but Cartesian theory rejected the absence of matter b/t to separate bodies

• Newton came w/ Universal Law of Gravity

• every particle of matter in the universe attracts every other particle with a force varying inversely as the square of the distance b/t them and directly proportional to the product of their masses

• Impact of Newton• Principia confirmed work of

Copernicus, Galileo, Kepler and heliocentrism

• Fueled a surge in science• Made a fundamental reconception

of the universe (Paradigm shift in the Weltanschauung)

Achievement of Newton: Promise of Science

Impact of Newton• His discoveries sparked the

founding of Institutionalization of knowledge

– Royal Society of London 1662– Royal Academy of Science

France 1666– Scientific periodicals and

journals• Practical applications

– Tidal movement– Timepieces (

Greenwich and the story of time John Harrison and the H4)

– Longitude• Maps

John Harrison's fourth marine timekeeper H4

• Calculus– military applications

• Improved firearms– calculus allowed an exactness to curves

and trajectories• Steam

– Boyles Law– Robert Boyle (1627-1691) used an air

pump and came up w/ Boyle’s law• under constant temperature the volume

of a gas decreases in proportion to the pressure placed on it

– Thomas Newcomen• Invented a Steam engine in 1702 with

limited application• Used by James Watt to develop steam

engine as we know it• Later Applied to government

Impact of Newton

Scientific Revolution and the world of thought• Science was called natural philosophy • Gap between Christianity and natural science

was widening• Caused a profound readjustment on human

view of himself• No longer the center of creation• Old cosmos comfortably enclosed and

ranked everything• Now humans were puny & insignificant

materials flying through endless space• Bible didn’t mention this

– Blaise Pascal, scientist and mathematicians terrified of this

• Most were optimistic

• Alexander Pope on Newton “Let Newton be and all was light”

• Human reason could conquer all• New view contributed to further secularization of European

society• Pushed religion to the side• The universe operates under natural laws• Is orderly and predictable• Contains natural rightness and justice• Ideas were more acceptable as a new view of the human

experience was emerging• Religion still strong

– Newton and Descartes wrote earnest tracts of the truth of religious doctrines

– Descartes (who questioned everything) said that the customs of one’s country were to be accepted without question

Scientific Revolution and the world of thought