Physical Science

• Disappearing Ships


  • If the Earth was flat then a ship traveling away from an observer should become smaller until it disappeared
  • The Greeks observed that the ship became smaller and then its hull disappeared first before the sail as if it was being enveloped by the water until it completely disappeared
• The Greeks observed the disappearance of ships


  This suggested the Earth was not flat
• The Shape of the Sun and the Moon

  • Aristotle argued that if the Moon and the Sun were both spherical then perhaps, the Earth was also spherical
• Aristotle proposed the Earth was spherical based on the shapes of the Sun and Moon
• North Star


  • The North Star was believed to be at a fixed position in the sky
  • When the Greeks traveled to places nearer the equator, like Egypt, they noticed that the North Star is closer to the horizon
• The North Star appearing closer to the horizon as you travel towards the equator

  Suggests the Earth is not flat
• Most Greeks believed the Earth was round, not flat


  Around 500 BC
• Pythagoras and his pupils

  • They were first to propose a spherical Earth
• Anaxagoras further supported the proposal of a spherical Earth through his observations of the shadows that the Earth cast on the Moon during a lunar eclipse

  500 to 430 BC
• Celestial domain


  Perfect, made up of the perfect substance "ether", can only move in perfect circular motion at constant speed
• Diurnal/daily motion of the sky

  1. Appearance that objects in the sky move relative to the Earth's local horizon (celestial objects: moon, Sun, stars, planets; there were only five known planets: Mercury, Venus, Mars, Jupiter, Saturn)

  2. Observed for one whole day at the same location on Earth
• Annual motion of the sky

  1. Appearance that objects in the sky move relative to the background stars

  2. Observed at the same time of the day and at the same location on Earth
• Terrestrial domain


  • Imperfect, tendency of things to attain perfection is the cause of their motion
  • Things move towards the center of the Universe (center of the Earth) or away from it based on their composition of the elements (fire, air, water, earth)
• The Greeks made major contributions in different fields, including philosophy, science and mathematics
• Pythagoras


  Believed the stars, planets, sun, and moon were attached to crystalline spheres which rotated around the Earth (Geocentric model)
• The five known planets were Mercury, Venus, Mars, Jupiter, Saturn
• Plato


  • Believed the attainment of perfection is the absence of change
  • Mathematical symmetries demonstrate perfect shapes (sphere and circle)
  • Celestial spheres being crystalline and containing the moon, the Sun and the stars
  • The daily and annual patterns of the sky must have a greater reality besides its appearance
• Plato believed the entire cosmos was precisely formed with geometric shapes and that they were the key to understanding the mysteries of the universe
• Eudoxus


  Followed previous models of the universe but added auxiliary spheres to provide appropriate tilt to the planets' path
• Aristotle


  • Believed the Earth is motionless at the center of the universe and all the stars and planets revolved around it
  • Stars and planets moved in circular paths (Geocentric model)
• Retrograde motion of planets

  1. Necessitates the addition of more mechanisms called "devices" to produce the visual motion of the planets

  2. Combination of deferent and the epicycles is the most practically accurate device during that era
• Hipparchus measured the length of the year to within minutes of the modern value
• Aristarchus proposed that the earth rotates around the sun
• Precession of Equinox


  1. Position of the stars shifted in a systematic way from earlier Babylonian measures (Hipparchus)

  2. Observable phenomena of the rotation of the heavens, a cycle which spans a period of approximately 25920 years
• Shape of the Earth according to ancient Greeks

  Flat disc
• Possible shapes of the Earth according to ancient Greeks

  • Cylinder
  • Octagon
  • Flat disc
  • Sphere
• Shape of the Earth as described by modern astronomy

  Oblate spheroid
• Possible shapes of the Earth as described by modern astronomy


  • Ellipsoid
  • Oblate spheroid
  • Hyperboloid
  • Oblate paraloid
• Events where the circular shadow of the Earth can be observed

  • Solar eclipse
  • Lunar eclipse
• Events where the circular shadow of the Earth can be observed

  • Solar eclipse
  • Summer solstice
  • Lunar eclipse
  • Winter solstice
• Position of the North Star if you go nearer the equator

  Farther away from the horizon
• Possible positions of the North Star if you go nearer the equator

  • Closer to the horizon
  • The North Star is fixed wherever you are on the Earth
  • It disappears completely
  • Farther away from the horizon
• What can be observed of a cruising ship if the Earth is a flat disc

  It will become smaller and smaller until it disappears
• Possible observations of a cruising ship if the Earth is a flat disc

  • It will shrink then only the sail will be visible until it completely disappears
  • It will become bigger and bigger
  • It will not change its size
  • It will become smaller and smaller until it disappears
• Evidences that the Earth is spherical according to Greeks


  • Rising and setting of the Sun in the east and the west, respectively
  • Point where the Sun rises and sets in the horizon varies in a year
  • Phases of the Moon
  • Lunar eclipse
  • Daily and annual motion of the stars
  • Planets Mercury, Venus, Mars, Jupiter, and Saturn
• Motion


  The ability of an object to change its position with respect to its surroundings in a given time
• Motion is always observed and measured with a point of reference
• All living things show motion whereas non-living things show motion only when force acts on it
• Types of motion


  • Linear motion
  • Rectilinear
  • Curvilinear
  • Circular motion
  • Rotary motion
  • Oscillatory motion
• Aristotle


  An ancient Greek philosopher and polymath whose writings cover a broad range of subjects including physics, biology, zoology, metaphysics, logic, ethics, aesthetics, poetry, drama, music, rhetoric, psychology, linguistics, economics, politics, meteorology, geology, and government