Chapter 2 Flashcards
retrograde motion
the apparent motion of a planet (as viewed from earth, during the period of a few weeks to a few months) when it moves westward relative to the stars in our sky.
scientific model
a representation of some aspect of nature that can be used to explain and predict real phenomena without invoking myth, magic, or the supernatural
scientific theory
a model of some aspect of nature that has been rigorously tested and has passed all tests to date
what was Ptolemy known for?
Ptolemaic model that stated that the earth was the center of the universe with planets moving around Earth on small circles that turned around larger circles. had retrograde motion
parallax
the apparent shifting of an object against the background, due to viewing it from different positions
What was Copernicus known for?
in his book, he revived aristarchus’s radical suggestion of a Sun-centered solar system and described the idea with lots of mathematical detail.
What was Tycho known for?
over a period of three decades he used his naked-eye observatories to measure planetary positions within 1 minute of arc (1/60 of a degree)
What is Kepler’s first law of planetary motion
“The orbit of each planet around the Sun is an ellipse with the Sun at one focus”. closest to sun at perihelion and farthest at aphelion.
what is the length of the semimajor axis?
the average of a planet’s perihelion and aphelion distances= average distance from the sun
what is Kepler’s second law of planetary motion?
“As a planet moves around its orbit, it sweeps out equal areas in equal times.” This means that the planet moves a greater distance when it is near perihelion than it does in the same amount of time near aphelion. This also means it moves faster when it is nearer to the sun and slower when it is farther from the Sun.
What is Kepler’s third law?
p^2 = a^3
basically that farther planets orbit the sun at slower average speeds, obeying this mathematical relationship above
What evidence did Galileo find for the heliocentric model?
he observed four moons orbiting Jupiter, not earth. later, he observed that Venus goes through phases in a way that proved that it must orbit the Sun and not Earth.
What is Newton’s first law of motion
an object moves at constant velocity unless a net force acts to change its speed or direction. ex: a spaceship needs no fuel to keep moving in space
What is Newton’s second law of motion?
force = mass x acceleration. ex: a baseball accelerates as the pitcher applies a force by moving his arm.
What is Newton’s third law of motion?
For any force, there is always an equal and opposite reaction force. ex: a rocket is propelled upward by a force equal and opposite to the force with which gas is expelled out its back.
Occam’s razor
the idea that scientists should prefer the simpler of two models that agree equally well with observations
pseudoscience
something that purports to be science or may appear to be scientific but that does not adhere to the testing and verification requirements of the scientific method
what is the cosmological principle
Newton’s “one universe” philosophy that stated that the entire universe must obey the same rules.
gravitational lensing
Curved spacetime alters the paths of light rays, shifting the apparent positions of objects in an effect called gravitational lensing.
limitations of rubber sheet analogy
can’t see the warping of the “rubber sheet” irl; masses do not “rest” upon spacetime like they do on a rubber sheet; rubber sheet only shows two dimensions of space
black hole
object whose gravity is so powerful that not even light can escape it
what is the rubber sheet analogy?
mass of sun curves spacetime; freefalling objects near sun follow curved path; circles near sun have circumference less than 2πr.
Einstein’s gravity
mass warps spacetime; massive objects curve spacetime while other objects simply follow the curvature much like the marbles following the contours of a bowl. “gravity is the curvature of spacetime”
spacetime
where all objects reside in; four-dimensional
momentum
mass x velocity
angular momentum
momentum gained from rotation or revolution; mass x velocity x radius
conservation of angular momentum
in the absence of net torque (twisting force), the total angular momentum of a system remains constant
center of mass
the balance point for all the mass of a system
