bellwork 1.who is credited with the revolutionary model of a heliocentric solar system? a. aristotle...
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Bellwork
1. Who is credited with the revolutionary model of a HELIOCENTRIC solar system?
A. AristotleB. PtolemyC. GalileoD. Copernicus
2. The planets loop backwards in their orbits.A. TRUEB. FALSE
3. During which months is Earth closest to the Sun?
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The story so far….• Ancient Greeks had a GEOCENTRIC model of the solar system
with Earth in center and Sun and planets in perfect circles.• Ptolemy add many epicycles to explain the looping of planets
during retrograde motion.• Galileo used a telescope to see phases of Venus, Jupiter’s
moons, rotating sunspots• Copernicus made a HELIOCENTRIC model of the solar system
with the Sun in the center so the planets were NOT looping backwards, Earth’s faster orbit was ‘passing’ the slower outer planets.
http://www.classzone.com/books/earth_science/terc/content/investigations/es2603/es2603page01.cfm3
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Kepler’s Model of the Solar System
Tycho Brahe (1575)
After seeing the total eclipse on August 21, 1560, and became a master of careful astronomical OBSERVATIONS.
Lost part of his nose in a duel and replaced it with a metal one.
Made DETAILED naked eye observations of the motions of the planets.
In the course of 30 years, he had amassed the most accurate astronomical DATA of the day
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Mathmatician - Kelper's mathematical skills were extraordinary.
He could not get Tycho's very careful observations to fit Copernicus’ model.
He constructed 3 Laws about planets orbits:
SHAPE, SPEED, TIME
Kepler ‘inherited’ the observations after the sudden death of Tycho
Johannes Kepler’s (1600)
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Kepler’s 3 Laws of Planetary Motion
1st Law: Ellipses!
The SHAPE of the orbital paths of each planet is an ellipse (NOT a perfect circle)
(with the Sun not exactly in the center, but at one focus)
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http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::800::600::/sites/dl/free/007299181x/78778/Kepler_Nav.swf::Keplers%20Second%20Law%20Interactive 8
2nd Law: SPEED of the planet
An imaginary line connecting the Sun to any planet sweeps out equal areas in equal time.
Area 2
Area 1
90 days
90 daysPlanets have
variations in their orbital
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Kepler’s 3rd Law:
a planet’s orbital TIME is proportional to its distance.
P2 (years) = A3 (AU)
1 Astronomical Unit = The Earth-Sun Distance (93 million miles)
In other words……the farther away the planet, the longer its ‘year’
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Kepler’s Third LawObject a (AU) P (year) a3 P2
Mercury 0.387 0.241 0.058 0.058
Venus 0.723 0.615 0.378 0.378
Earth 1.00 1.00 1.00 1.00
Mars 1.52 1.88 3.51 3.53
Jupiter 5.20 11.9 141. 142.
Saturn 9.54 29.5 868. 870.
Uranus 19.2 84.0 7,080. 7,060.
Neptune 30.1 165. 27,300. 27,200.
Pluto 39.5 248. 61,600. 61,500.
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Heliocentric Solar System
Using data construct a model to show the correct SIZE and SCALE
Isaac Newton (1642 – 1727)
One of the most brilliant theoreticians to ever live.
Explained WHY the planets move as they do.
He formulated three laws of motion and the law of universal gravitation.
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Newton’s 1st Law of Inertia:Objects in uniform straight line motion continue in straight line motion unless an outside force is applied to change their motion
Once in orbit, a planet will continue its orbital motion at constant velocity until an outside force (asteroid,
another planet?) acts on it to change its orbit.
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Newton’s Second Law
The ACCELERATION (change in motion) of an object is directly proportional to the net FORCE acting on the object, is in the direction of the net force, and is inversely proportional to the MASS of the object.
a = Fnet
massOR
F = ma
WHY
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Newton’s Third Law
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.
“To every action there is an equal and opposite re-action.”
Forces are interacting in PAIRS – one object on another
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Law of Universal Gravitation
Mass attracts mass
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R
MGMF
Gravity is the FORCE that causes objects to move!17
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