OPENING QUESTIONS:
1) The Earth revolves around the sun clearly showing principals of angular momentum and rotational dynamics. Why? (Hint: it's more than the sun's gravity)
2) Is the Earth's orbit more like an elipse or more like a circle? (hint: Think again)
Hint #2: a circlar orbit has an eccentricity of 0, an eliptical orbit has an eccentricity between 0 and 1, a parabolic orbit has an eccentricity of 1 and a hyperbolic oribit has an eccentricity of > 1════════════════════════
It's kind of surprising, the earth's oribt is very nearly circular with an eccentricity of only 0.0167 (according to Univ of Georgia Hyperphysics)
OBJECTIVE:
1) I will be able to apply Kepler's 3 Laws to planetary motion after today's class.
WORDS/FORMULAE FOR TODAY:
- "G" vs "g"
- Fg = Gm1m2/r2
Kepler's 1st: All planets move in elipses with the sun at one focus.
Kepler's 2nd: Planet's orbits sweep out equal orbits in equal times:
- mathematically speaking that's dA/dt = constant
Kepler's 3rd: The (magnitude) of the square of the period of a planet's orbit is preportional to the (magnitude) of the cube of the (average) distance from the sun:
- Or in other words: T2α R3
- Or with the preportional constant: T2= KsR3
WORK O' THE DAY:
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Teachable Moments: Academic Honesty
One of the main benefits of the GOOGLE phenomenon is also a major problem with the google phenomenon....
Mr W rants...
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Now comes the historical part of our course..well, sorta.
Kepler was a German astronomer who built on the works of Copernicus (who move science away from an Earth-centered Universe to a sun-centered Universe) and helped prepare the way for Newton.
Through diligent observations and astute mathematics, Kepler determined 3 universal Laws of Planetary Motion (I dunno, do LAWS come in 3's??? I mean there are 3 of Newton's Laws, 3 Kepler Laws, and certain 3 Laws of Robotics... right?
Anyhow...
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Take look at page 398...
There's some kinda cool stuff there, let's discuss briefly
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HOMEWORK:
Chapter 13 problems begining on page 411:
17 (rotational dynamics also works well here), 18, 23, 26 (yup, do this one!)