PHY100H5 Study Guide - Fall 2018, Comprehensive Midterm Notes - Earth, Physics, Gravity
PHY100H5
MIDTERM EXAM
STUDY GUIDE
Fall 2018
Chapter 1: Of Atoms and Stars
The Earth-Centered Universe
- Ancient Greeks (Pythagoras, 500 BCE): sun, moon, 5 visible planets, and the stars are
attached to 8 transparent spherical shells centered on Earth
- Used their own observations to draw this conclusion
- This hypothesis predicated that each planet rotated uniformly around Earth
- However, observations contradicted this: Mars shows retrograde otio it’s ot just
oig i circles, it’s oig at arious rotations at certain times)
The Earth-Centered Universe
- Ancient Greeks (Pythagoras, 500 BCE): sun, moon, 5 visible planets and the stars are
attached to 8 transparent spherical shells centered on Earth
- This hypothesis predicted that each planet rotates uniformly around the Earth
- Observations contradicted this: Mars shows retrograde motion
Circles Moving Around in Circles
- The epicycle-deferent theory explained the retrograde motion of the planets and their variable brightness
- Epicycle is when something is rotating on its own axis
- Deferent is when something is rotating on another axis
- This theory was perfected by Ptolemy around 100 CE and survived for 14 centuries
- When a planet is closest, it appears brightest (on the deferent cycle) and when a planet is
farthest, it appears dimmest (on the epicycle)
Copernicus: Less is More
- Ptole’s sste lacked elegace: ore tha epiccles for each plaet
- If everything can move, what is the simplest geometrical scheme that agrees with the observations?
- Copernicus (1543): planets (including earth) rotate uniformly around the sun, only the moon orbits Earth (a
natural satellite)
- The closer planets to the sun have smaller circumferences to rotate than Earth does (they will eventually surpass
Earth because they have less area to cover)
Which Theory is True?
- Tcho Brahe easured the plaets’ positios ith uch higher accurac
- The position and order of the plaets i Ptole’s theor as’t accurate, as
he Brahe ade diagras of the plaets, Ptole’s theor did’t fit properly
- The new data acquired by Brahe disagreed with both Copericus’s ad Ptole’s
theories (despite being an avid Copernican theorist)
- Instead of rotating in circles, the planets rotated in ellipses (instead of one focus,
ellipses have two foci)
- Kepler’s theor 6: the planets move on sun-focused ellipses
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- An oval (egg-shaped) orbit around the sun that still holds true today
Science: a Dialogue Between Nature and Mind
- Observation: can be qualitative, quantitative (measurement), or
designed (experiment)
- Theory: a well-confirmed, but refutable set of ideas that explain the
current observations
- Model: a theory that we can visualize
- Principle or law: on idea within a theory
- Hypothesis: a reasonable but unconfirmed scientific suggestion; an
intelligent guess (THIS IS NOT A THEORY)
- If a theory is not supported by evidence, the theory must be altered to
make sense of the evidence
- No theory is 100% certain because there is the possibility an
observation will later refute it
- If a theor does’t eplai the universe or cannot be tested t is not a
theory at all
- Hypotheses can be based on already known evidence and
observations
True or False?
- the Earth is round: true
• ships on horizons gradually disappear out of your line of vision
• the altitude of the sun at certain times varies at different hemispheres of the Earth
• new technology confirm theories (pictures of Earth)
- the position of the stars influence the personality of humans on earth: no evidence to
say either way
• there is no scientific evidence that proves the position of stars has influence of
the personality of people
• there is more gravitational force acting upon a child during childbirth than any
force being acted upon it by the planets and their positions
- in a previous life I was a cricket: no evidence to say either way
- we are all alone in the universe: no evidence to say either way (scientifically viewed)
- no humans live forever/all humans live forever: no evidence to say either way (in terms of science)
The Copernican Revolution
- there is symmetry everywhere (atoms have a nucleus in the center, with electrons rotating around it; the sun is
the center of our galaxy and there are planets rotating around it)
- the Earth is just a planet, like other planets
- our sun is just a star like other stars and our galaxy is just one from 100 billion
- the laws of nature are universal, humanity is not the center of the universe
- the same systems are repeated from microscopic levels to macroscopic levels
Pseudoscience
- id pollutio rooted i igorace sugar-coated i science)
- appears scientific even though there is lack of supporting evidence and plausibility
-
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