Week 4 Lectures

Question 1

WhichstatementaboutancientGreekastronomersis correct?

Answer 1

They performed a test to see whether Earth went around the Sun but misinterpreted what they saw.

Question 2

First to reject previous Ptolemaic model on purely empirical (as opposed to philosophical) grounds – it didn’t match the observations well enough, so there must be a better model!
• Made a model with lots of epicycles (circles on circles on circles). Not pretty, but mathematically rigourous, and better match to observations.

Answer 2

Ibn Al-Shatir

Question 3

First formal testable model with Sun at the center. Predictions about as good as Ptolemy’s.

Answer 3

Nicolaus Copernicus

Question 4

Heliocentric model that matched observations better than Copernicus’s, using elliptical orbits.

Answer 4

Johannes Kepler

Question 5

was ultimately responsible for acceptance of heliocentric model.

Answer 5

Success of Kepler’s predictions matching the observations

Question 6

Kepler’s First Law

Answer 6

— Planets orbit in elliptical
orbits with the Sun at one focus.

Question 7

Kepler’sSecondLaw

Answer 7

Planets sweep out equal areas in equal time (i.e. they move faster when closer to the Sun).

Question 8

Which statement is correct about how fast the Earth moves around the Sun?.

Answer 8

A. It moves fastest in January

Question 9

Kepler’sThirdLaw

Answer 9

Innerplanetshaveshorteryears than outer planets, with a precise mathematical relationship between orbital distance and period

Question 10

Made major improvements to the recently-invented telescope, and turned it
up to the sky!

• A few key observations and experiments convinced remaining
doubters.

Answer 10

Galileo Galilei

Question 11

Galileo’s Discoveries

Answer 11

Demonstrated that we feel acceleration, not motion. Answered “why don’t we feel like we’re moving?” objection.
2. Observed all phases of Venus, so Venus must sometimes be behind the Sun.
3. Discovered moons of Jupiter. (proved that Earth is not the center of everything)

Question 12

Galileo’s Legacy

Answer 12

• According to the Catholic Church’s interpretation at the time, the Earth must be at the center of the Universe. They forced him to recant his views (1633) and put him under house arrest.
• By 1700, Kepler’s model + Galileo’s observations had convinced everyone (incl. Catholic Church by 1750s, though they didn’t officially pardon him until 1992!).

Question 13

Goal of Scientific Method

Answer 13

Prove theories false

Question 14

describe how planets orbit the Sun (and how the Moon orbits Earth, exoplanets orbit their stars)

Answer 14

Kepler’s Laws

Question 15

push or pull on an object that modifies its motion.

Answer 15

force

Question 16

Matter attracts other matter. The force of attraction depends on the
mass.

Answer 16

Gravity

Question 17

+/- electrical charges. Opposite charges attract, like charges repel, moving charges get pulled sideways.

Answer 17

Electromagnetism

Question 18

Very short-range force that keeps the nucleus of an atom stable.

Answer 18

Strong Nuclear Force

Question 19

Very short-range force responsible for radioactive decay of nuclei.

Answer 19

Weak Nuclear Force

Question 20

Fundamental Forces

Answer 20

Gravity
Electromagnetism
Strong Nuclear Force
Weak Nuclear Force

Question 21

Keeps things from floating away from the Earth

Answer 21

Gravity

Question 22

–Everything else!!!

Answer 22

Electromagnetism

Question 23

Gravity is

Answer 23

Very weak