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 MotionNo. 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 MotionNo. 3:

TA2 = rA

3

TB2 rB

3

WhereTA = period of planet ATB = period of planet BrA = avg. distance of planet A from sunrB = 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 4th moon, had a period of 16.7 days. Using the same units that Galileo used, predict Callisto’s distance from Jupiter.

Galileo (1564-1642)

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 whichkeeps the Moon in orbitaround the Earth is thesame force that attractsall objectsto Earth.

Sir Isaac Newton (1642- )

Major Philosophical Shift!

TERRESTRIAL CELESTIAL

Terrestrial and Celestial MotionObey 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 ~ mA mB / d2

Law of Gravitation

Fc = Fg

mE v2 = G mE mS

r r2

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 elevatorCan’t tell if she is on earthAt rest or in deep space And accelerating at 9.8 m/s2 !

The End: worksheets follow