Announcements

• 1st Quarter observing night tonight. Meet in the hallway in front of B-3210 around 6:45pm.

• Exam 2 is scheduled for Wednesday March 4 (next Wednesday). Will cover Chapters 1, 2, 3 & 4 of Foundations of Modern Cosmology. Sample questions for Chapter 4 have been posted.

• Projects: since the topic must be approved before spring break, submit a topic/title with a two or three sentence abstract by next Wednesday. This will be worth 5% of the project grade.

Newton’s Mechanical Universe

Isaac Newton (1643 – 1727)

Newton’s home: Woolsthorpe in Lincolnshire

Newton’s most

important work

Newton was 43 years old when the Principia was finally published. Most of the work for it was done when he was in his early 20’s

Newton’s First Law: The Law of Inertia

An object in uniform motion (straight line at constant speed) will maintain that motion unless acted on by some external force.

Newton’s Second Law: The Force Law

The acceleration an object experiences is directly proportional to the net force acting on it and inversely proportional to the objects mass.

F = ma

Newton’s Third Law: The Action-Reaction Law

For every force there is an equal and opposite reaction force.

Newton’s Law of Universal Gravitation

Two bodies attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers

Newton related the acceleration experienced by a falling apple to

that experienced by the moon

applemoon

EarthmoonEarth

aa

rr

36001

60

Galileo had measured the acceleration of a falling body near the surface of the Earth. Newton calculated the acceleration needed to keep the moon in orbit (centripetal acceleration).

A few colored card questions

ClassAction website Renaissance Astronomy module

Gravity Fundamentals…options 1 & 3Gravity Directions…both optionsEarth Force vs. Sun ForceForces and Motion

Discussion Questions:Applying Newton’s Laws 2

Five minute Essay

Both Newton and Aristotle said that the Moon goes around the Earth. Describe how each of them explained why the Moon orbits the Earth and the difference between their explanations.

Newton’s rival, Robert Hooke, also

theorized that gravity was an inverse square law

Newton’s genius was to apply gravity universally and to prove it

Newton also related the gravitational force to the mass of the objects

Galileo’s Law of Falling Bodies said all bodies fall with the same acceleration. Newton showed why.

Newton’s cannon demonstrates what is required to reach orbit

Check out Newton’s cannon applet

Newton’s theories of mechanics and gravitation required a universe

that was infinite

Henry Cavendish (1731 – 1810) was the first to measure “G” in 1798

2

2111067.6kg

mNG

The Age of the Universe begins to be a question for science

Geologists are beginning to study structures that lead them to an age for the Earth as “very old”

Darwin’s theory of Evolution requires an “old” Earth

Obler’s Paradox

Why is the sky dark?

The nature of matter: ChemistryDeveloped by Dmitry Mendeleev and Lothat Meyer in 1869

The “Plum Pudding” atomic model

Developed by J. J. Thompson to explain how electrons and protons were distributed. Neutron had not yet been discovered

Rutherford performed experiments that bombarded gold foil with alpha

particles

The Rutherford Atom The Nucleus

Protons(Neutron still

not discovered)

Surrounded by electrons in solar system

like orbits

According to Maxwell’s

Electromagnetic Theory an

electron in orbit must radiate

energy

Along comes Quantum Mechanics

Head mechanic: Niels Bohr

The Universe according to Quantum Mechanics

• You can’t tell precisely where anything is.

• You can’t tell precisely how fast anything is moving.

• Particles act like waves.

• Waves act like particles.

• Particles can pass through “solid walls”

• A very non-deterministic universe completely contrary to Newton’s mechanical universe