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
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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.
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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