Announcements 1 st 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 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 & 3 Gravity Directions…both options Earth Force vs. Sun Force Forces 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

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: Chemistry Developed 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