Chapter 3 - Chapter 4 (Week 3) Flashcards
What were some Western astronomy theories before Copernicus?
- stars, sun, and moon rise and set every day
- Earth doesn’t feel like its moving
Conclusion
Earth is the center of the universe (geo-centric model)
What is a retrograde motion and how did it come to be?
Ptolemy’s model first gave light to the retrograde motion idea. This is because he plotted mars’ position in relation to background stars which gave the idea that mars’ orbits the earth with a retrograde motion
What is a helio-centric model
helio-centric models depict the sun as the center of our solar system as opposed to the earth which many believed in the past to be the case.
Who was Tycho Brahe
he searched for Stellar parallax, as the earth orbits the sun, nearby stars should appear to shift positions relative to background stars. brache’s observations failed to measure parallax so the conclusions:
- Earth’s position is fixed
- the stars are extremely distant
What was Kepler’s first law?
the orbit of each planet around the Sun is an ellipse with the sun at one focus
What is a semi-major axis of an ellipse
the semi-major axis is half of the major axis of an ellipse
What is Kepler’s second law?
As a planet moves around its orbit it sweeps out equal areas at equal times. Meaning that a planet travels faster when its nearer to the sun and slower when it farther away from the sun
What is Kepler’s thrid law?
More distant planets orbit the sun at a slower average speed, obeying the relationship:
p^2=a^3
where
p= orbital period in years
a= average distance from the sun in AU
What supported the heliocentric model
Galileo used a telescope and observed that Jupiter has 4 moons around it therefore the Earth cannot be in the center of everything.
Why was the helio-centric model preferred
explains retrograde notion of the planet
explains the phases of Venus
makes accurate prediction of the position of the planets
What are Newton’s laws of motion and gravity?
- an object will remain at a constant velocity unless acted upon by a net force.
- Net force = mass x acceleration
- Every force cause an “equal and opposite” reaction force
The universal law of gravitation
F=G((m1*m2)/()d^2))
What is Newton’s version of Kepler’s 3rd law?
p^2 = (a^3)/(m1+m2)
What is Momentum
momentum = mass x velocity
A net force changes the momentum, usually by causing an acceleration (Changing velocity)
Does the planet’s momentum change?
yes but so does the stars which means that the total momentum of the system is conserved.
