Quiz 2 review giants of science ch 2 gravity and motion ch 3 light and atoms ch 4
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Quiz #2 Review Giants of Science (Ch. 2), Gravity and Motion (Ch. 3) Light and Atoms (Ch. 4). Thursday 29 September 2011. Also study the Quiz 1 recap notes. What to Know from Chapter 2.

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Quiz 2 review giants of science ch 2 gravity and motion ch 3 light and atoms ch 4

Quiz #2 ReviewGiants of Science (Ch. 2), Gravity and Motion (Ch. 3)Light and Atoms (Ch. 4)

Thursday 29 September 2011

Also study the Quiz 1 recap notes


What to know from chapter 2
What to Know from Chapter 2

  • The accomplishments of the different astronomers from the ancient Greeks to Copernicus, Brahe, Kepler, and Galileo

    • What they knew and how they knew it.

    • What technological advances led to what discoveries

  • The difference between the geocentric and heliocentric models of the solar system

    • Arguments for and against the two models

    • Final arguments in favor of the heliocentric model

  • Kepler’s laws


What the giants of science accomplished
What the Giants of Science Accomplished

  • Measured quantities of the solar system

    • Earth shape and size

    • Moon and Sun sizes and distances

    • Planet-Sun distances determined relative to Earth-Sun distances

  • Technological advances led-to and required changes in solar system model

    • Move from Earth-centered (geocentric) model to Sun-centered (heliocentric) model


Shape of the earth is spherical aristotle
Shape of the Earth is Spherical Aristotle

  • Earth shadow is always circular, never oval or linear, during a lunar eclipse

  • Observers at different latitudes see different stars and constellations at the same time.


Size of moon distances to moon and sun aristarchus
Size of Moon – Distances to Moon and Sun -- Aristarchus

  • During lunar eclipse, found that apparent moon size was 1/3 of Earth shadow.

  • Distance to Sun is greater than distance to moon.

  • Size of Sun is greater than Earth or Moon

  • Proposed heliocentric model, but his contemporaries rejected that model since stellar parallax was not observed.


Size of earth erastothenes
Size of EarthErastothenes

  • Derived angle of incidence for Sun’s rays based on shadow length in Alexandria—no shadows in Syene at time of observation.

  • Angle between cities is same as Sunlight angle (from geometry)

  • Know distance between cities

  • Derive Earth circumference (and radius) from geometry


Derive planet sun distances copernicus
Derive Planet-Sun Distances Copernicus

  • Inner-Planet-Sun distances can be derived relative to Earth-Sun distance using geometry when planet is at greatest elongation.

  • Outer-Planet-Sun distance: start at opposition,

    • (1) mark time that elapses until Sun-Earth-planet angle is at 90°,

    • (2) derive fraction of orbits traversed,

    • (3) used geometry to find Planet-Sun distance relative to Earth-Sun distance


Geocentric vs heliocentric models
Geocentric vs. Heliocentric Models

  • Arguments for the Geocentric model

    • Can not observe stellar parallax

    • It does not feel like we (on the Earth) are moving

    • Idea that the heavens are fixed and unchanging


Geocentric earth centered model eudoxus
Geocentric (Earth-centered) ModelEudoxus

  • Model: Earth at the center, then Moon, Venus, Mercury, Sun, Mars, Jupiter, Saturn

  • Problem: Can not explain apparent retrograde motion of planets

    • Lower figure shows actual heliocentric model


Geocentric earth centered model ptolemy
Geocentric (Earth-centered) ModelPtolemy

  • Model: Earth at the center, then Moon, Venus, Mercury, Sun, Mars, Jupiter, Saturn

  • Solution(?): Invoke epicycles to explain apparent retrograde motion of planets

    • Lower figure shows actual heliocentric model


Heliocentric model copernicus
Heliocentric ModelCopernicus

  • Moon orbits Earth; Mercury, Venus, Earth, Mars, Jupiter and Saturn orbit the Sun

  • Planetary orbits are circular; a planet moves at a uniform speed throughout its orbit (?)

  • Good: Derived good distances between planets and Sun

  • Good: Explains apparent retrograde motion of planets

  • Bad: Poor predictions of where planets will be in the future, still need epicycles.


Heliocentric model kepler
Heliocentric Model Kepler

  • Major technological advance: high precision instruments for measuring angles, data set of full-time professional astronomer Tycho Brahe

  • Orbits are elliptical with Sun at a focus

  • A line between the Sun and a planet sweeps out equal areas in equal times

    • Or, a planet moves faster when is closer to the Sun, and slower when it is further from the Sun

  • When comparing different planets: the square of a planet’s orbital period is proportional to the cube of its semi-major axis (P2 = a3)

    • Planets with smaller orbits (closer to the sun) complete their orbits faster than planets with larger orbits.


Kepler s laws
Kepler’s Laws

A planet sweeps out equal areas in equal time periods throughout its orbit. This occurs because a planet moves slower when it is far from the Sun, and faster when it is near the Sun

A planet’s orbital period depends on it’s distance from the Sun. A planet closer to the Sun has a shorter orbital period than a planet far from the Sun.

Planets orbit the sun in elliptical orbits with the Sun at one of the two focus points.


Heliocentric model galileo
Heliocentric Model Galileo

  • Major technological advance: the telescope (at this time, a spyglass)

  • Observed mountains on Moon

    • concluded Moon was rocky like Earth

  • Venus shows gibbous phases, must orbit the Sun

  • Jupiter has moons like Earth

    • Not everything revolves around Earth



What to know about gravity and motion
What to Know About Gravity and Motion

  • Difference between

    • Mass (an intrinsic property of an object), and

    • Weight (the force one object exerts on another)

  • Newton’s Universal Law of Gravitation

    • Underlying force responsible for Kepler’s Laws

    • Newton’s modified version of Kepler’s third law is an extremely powerful tool

      • Can find mass of the Sun from the orbital periods of the planets

      • Can find masses of binary stars from their orbital period or orbital velocities

      • Can find the mass of a galaxy from the orbital velocities of the stars, gas, and dust within it


What to know about gravity and motion1
What to Know About Gravity and Motion

  • Surface Gravity

    • The acceleration a mass undergoes at the surface of a celestial object (e.g., an asteroid, planet, or star)

  • Escape Velocity

    • The speed required for an object to overcome a celetial object and escape into space


The universal law of gravitation
The Universal Law of Gravitation

  • Every particle in the Universe attracts every other particle.

  • The force of attraction increases as their separation decreases

    • Likewise the force decreases as their separation increases

  • The force of gravity follows an inverse square form:

    • If the separation increases by a factor of 2, the force decreases by a factor of 4

    • If the separation increases by a factor of 3, the force decreases by a factor of 9

    • If the separation increases by a factor of 4, the force decreases by a factor of 16

    • Etc.


Gravity holds the planets in their orbits
Gravity Holds the Planets in Their Orbits

  • Gravity is the force that is responsible for Kepler’s Laws


Surface gravity
Surface Gravity

  • Surface gravity is the acceleration a mass undergoes at the surface of a celestial object (e.g., an asteroid, planet, or star)

    • Depends on mass and radius of celestial body

  • Surface gravity:

    • Determines the weight of a mass at a celestial object’s surface

      • i.e., explains why you would weigh less on the Moon than on the Earth.

  • Influences the shape of celestial objects

  • Influences whether or not a celestial object has an atmosphere


Escape velocity depends on radius and mass of celestial body
Escape Velocity:Depends on Radius and Mass of Celestial Body


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