A Brief History of Classical Physics (Natural Philosophy)

Aristotle (c. 349 BC) Natural State of motion: rest. Force causes motion. Heavy objects fall faster. Natural State of motion: Circular Earth is the Center of the Universe TERRESTRIAL CELESTIAL

Nicholas Copernicus (1543) Natural State of motion: rest. Force causes motion. Heavy objects fall faster. Natural State of motion : Circular The Sun is the Center TERRESTRIAL CELESTIAL

Johannes Kepler (c. 1610) Earth Motion: Same as Aristotle Planets have elliptical orbits The Sun is the Center TERRESTRIAL CELESTIAL

Kepler’s Laws of Planetary Motion Law #1: The paths of the planets’ orbits around the sun are ellipses With the sun at one focus of the ellipse

Kepler’s Laws of Planetary Motion No. 2 A line from sun to planet sweeps out equal areas in equal time intervals Planets move faster when closer to sun Planets move slower when farther from sun

Kepler’s Laws of Planetary Motion No. 3: T A 2 = r A 3 T B 2 r B 3 Where T A = period of planet A T B = period of planet B r A = avg. distance of planet A from sun r B = avg. distance of planet B from sun

Example Prob. Kepler’s Law Galileo discovered the moons of Jupiter. He could measure their orbital sizes only by using the diameter of Jupiter as a unit of measure. He found that Io, which had a period of 1.8 days, was 4.2 units from the center of Jupiter. Callisto, Jupiter’s 4 th moon, had a period of 16.7 days. Using the same units that Galileo used, predict Callisto’s distance from Jupiter.

Galileo ( ) Law of Inertia: Uniform Motion Force causes change in motion All objects fall with the same acceleration Celestial Realm is imperfect Solar System is not unique TERRESTRIAL CELESTIAL

Sir Isaac Newton (1642- ) Quantified Galileo’s ideas Formulated Newton’s 3 Laws of Motion Gave mathematical expression to gravity with the Law of Universal Gravitation Gravity which keeps the Moon in orbit around the Earth is the same force that attracts all objects to Earth.

Sir Isaac Newton (1642- ) Major Philosophical Shift! TERRESTRIAL CELESTIAL Terrestrial and Celestial Motion Obey the same physical laws!! You mean: The same laws of Physics work everywhere!!? They are UNIVERSAL

Newton’s Law of Universal Gravitation The gravitational force between two bodies is Directly proportional to the product of their masses Inversely proportional to the inverse square of the distance between them F ~ m A m B / d 2

Law of Gravitation F c = F g m E v 2 = G m E m S rr 2

Albert Einstein (1916) General Theory of Relativity: Explained the cause of gravity through the concept of curved “space-time”

Albert Einstein (1916)..and also stated that: A uniform gravitational field is equivalent to a uniform acceleration. Therefore…. The lady in the elevator Can’t tell if she is on earth At rest or in deep space And accelerating at 9.8 m/s 2 !

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