PHYSCI

• Geocentric theory


  The structure of the solar system in which earth is assumed to be the center of it all
• Heliocentric theory


  The sun is assumed to lie at or near a central point while the earth and other bodies revolve around it
• Different descriptions of a flat earth can be found in the annals of ancient civilizations worldwide
• Thales


  • Pictured the earth as a flat disk floating on water
• Anaximander


  • Earth is a cylinder and its surface is curved
  • Earth is in the center
• Pythagoras


  • First to originate a spherical earth using observations
  • North and South Constellations
  • Sinking ships
  • Lunar eclipse
• North star was believed to be at a fixed position in the sky, but Greeks noticed it was closer to the horizon when traveling to places nearer the equator
• If the earth was flat, a ship traveling away from an observer should become smaller and smaller until it disappeared, but Greeks observed the hull disappeared first before the sail
• Pythagorean model


  • Geocentric
  • Earth is round
  • Heavenly bodies move in circle
  • Earth is at rest at the center, and everything rotates around it
  • "The music of spheres" motion of planets were mathematically related to musical sounds and numbers
• Plato


  • Earth is a form of globe having its extremes in every direction equidistant from the center
  • Universe is perfect or ethereal and unchanging
  • Stars embedded in the outer space are eternal and divine
  • "Saving the appearances" - what uniform and circular motion must be assumed for each of the planets to account for their apparently irregular annual paths
• Exodus of Cnidus


  • Homocentric model: celestial spheres share one common center - earth
  • First geocentric model
  • 27 interconnected geocentric spheres
• Aristotle


  • Earth is fixed at the center of the solar system and everything revolves around it
  • Proved the earth is spherical
  • All stars are fixed points which rotate on a single celestial sphere (65 spheres)
  • Primer mover: drives the motion of the planets
  • Added 3 spheres to Jupiter and Mars, 4 spheres to sun, moon, Venus, and Mercury
• Eratosthenes

  Ancient scholars tried to provide proof of a spherical earth and its circumferences through calculations, and Eratosthenes gave the most accurate size of the circumference
• Claudius Ptolemy


  • Earth is a spherical object
  • Stars are fixed bodies attached to a solid spherical exterior part of the universe
  • Planets moved independently of the fixed stars and sometimes seem to reverse their motion
• Ptolemy's Model


  • Geocentric
  • Shows the deferent (circular path which planets moves) and epicycle (circles where planets move)
  • Proposed the equant (a point close to the orbit's center)
• Aristarchus of Samos


  • Sun and the stars are fixed
  • First to place the sun at the center of the universe
  • Earth is revolving around the sun in a circular orbit
• Copernicus' corrections to the geocentric theory

  1. Proposed the heliocentric theorem

  2. Earth is considered as only one of the planets that move around the sun

  3. Earth rotates on its axis daily and revolves around the sun once a year

  4. Earth experiences an annual tilting of its axis

  5. The retrograde motion of the planets is explained by earth's motion

  6. The distance from the earth to sun is small compared to earth's distance from the stars
• Retrograde motion


  • Orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object
  • Motion of heavenly bodies is from west to east
• Copernicus' Model


  • Heliocentric
  • Celestial motions are uniform, infinite, and circular
  • Planets revolve around the sun
  • Earth's motion explains the retrograde of the other planets
  • Earth spins on a tilted axis, which accounts for the seasons
• Tycho Brahe's modifications to the geocentric model


  • Designed and built huge instruments used to make precise measurements of the positions of the planets
  • Discovered the supernova in the constellation cassiopeia in 1572
  • Made observations of planetary motions that are important to the development of Kepler's laws and other models of solar system
• Geo-heliocentric model


  History model of the universe was both heliocentric and geocentric, with the planets revolving around the sun, and the sun revolving around the earth
• Galileo's discoveries using his telescope

  1. Sunspots and rough surface of the moon

  2. 4 famous moons of Jupiter known as Galilean moons

  3. Venus has phases like moon
• Kepler's Laws of Planetary Motion

  • Orbits of the planets are ellipses, with the sun at one focus
  • An imaginary line drawn from the sun to a planet sweeps out equal areas in equal intervals
  • The larger the planet's orbit, the longer the revolution
  • The square of the revolutions of the planets are directly proportional to the cubes of their average distances
• Perihelion


  Point nearest to the sun
• Aphelion


  Point farthest to the sun
• Astronomical Unit (AU)


  Average distance between the earth and the sun, about 93 million miles or 150 million kilometers
• Aristotle's Theory of Motion

  • All objects on earth were believed to be a mixture of 4 elements (earth, water, air, and fire)
  • The velocity of a moving object is directly proportional to the force, and inversely proportional to the resistance created by the medium
  • The physics behind these heavenly bodies are different from things on earth
  • Celestial bodies move in a circular motion because this is the most perfect kind of unchanging eternal motions
  • Since there is perfection in the heavens, there can be no change, except for heavenly motions
  • The heavenly motions were part of the heavenly perfection and so by definition were not changes, but a type of constancy (hence the necessity for uniform circular motion)
  • Describes earth (sublunar realm) as chaotic and imperfect. The pure (perfect) elements, earth, air, fire, and water find themselves combined into the variety of substances in the physical world. These mixtures (imperfect substances) would want to be separated to become pure and perfect again
• Types of motion


  • Natural motion
  • Violent motion
• Natural motion


  • Exists in any type of motion that a body does naturally without forcing the motion to happen
  • Straight up and down
  • Without forcing the motion to happen
  • Happens spontaneously
• Aristotle's 4 Theories of motion

  • An object which is made up of an "Earth" material, falls toward the center of earth because it seeks its natural place
  • Heavy objects fall faster than the lighter ones
  • Objects fall faster in air than water
  • Objects sometimes move away from their natural places
• Violent motion


  • Exists when a motion requires a force to make an object move in "unnatural" manner
  • Disrupts the natural state
  • Impetus: the external action that cause violent action/motion
  • The action necessary to move things HORIZONTALLY
  • Does not happen without action
• Longevity of Aristotle's Theory of Motion


  • The theory was consistent with common sense
  • No other theories about motion were available during Aristotle's time
  • The quantitative method of observation to prove the validity was not yet developed
• Galileo


  Born in Pisa, Italy. He studied medicine at the University of Pisa then changed to Mathematics
• Galileo disproved Aristotle's claims and believed that the motion of objects is not simply due to the composition of objects</b>
• Galileo's Findings


  Motion can be describes by mathematics and the changes in some physical variable such as time and distance
• Horizontal motion


  1. An object in motion will continue to be in motion if unobstructed

  2. An external force is not necessary for it to maintain the motion

  3. A marble made to roll on flat surface would roll for an infinite amount of time
• Vertical motion


  1. In the absence of resistance, objects would fall not depending on their weight, but in the time of fall

  2. If the object encountered a resistive force from a fluid equal or greater than its weight, it will slow down and reaches a uniform motion until it reaches the bottom and stops

  3. A stone dropped in the ocean will sooner or later travel at constant speed

  4. The two object light and heavy, dropped simultaneously from the tower of pisa, fell and struck the earth at the same time
• Free fall motion


  • Free falling objects do not encounter air resistance
  • All free falling objects (on earth) accelerate downwards at a rate of 9.8m/s^2
  • It is a type of motion under the sole influence of gravity
• Vertical upward motion


  Follows a vertical upwards path resisting the effects of acceleration due to gravity
• Projectile motion


  1. A combination of uniform motion in the horizontal direction (Vx) and uniformly accelerated motion (Vy) in the vertical direction

  2. If it is not impeded, it will continue to move even without an applied force