physcience.1

• Flat Earth


  Early belief that Earth had corners and if you set sail straight in the ocean, you would get to the edge of Earth and fall
• Spherical Earth


  • Philosophers like Plato and Aristotle described Earth and the heavens as spherical
  • Navigators like Ferdinand Magellan and Juan Sebastian Elcano circumnavigated the world and proved that Earth is not flat

  
• Greek philosophers speculated that Earth was spherical


  6BCE

  
• Greek philosophers who theorized about the sphericity of Earth

  • Pythagoras (570 BCE – 490 BCE)
  • Eratosthenes (276 BCE – 194 BCE)

  
• Retrograde motion


  Apparent change in the movement of the planet through the sky
• Eudoxus of Cnidus' model


  • Explained the retrograde motion of the planets
  • Universe composed of Earth, five other planets (Mercury, Venus, Mars, Jupiter, and Saturn)
• Aristotle's model


  • Universe was spherical and finite
  • Earth was at the center of the universe and was stationary
  • Earth was composed of four elements: Earth, Water, Air, and Fire

  
• Geocentric model


  Model where Earth is at the center of the universe
• Aristarchus of Samos' model


  • First attempt to create a Heliocentric Model, which places the sun at the center of the Universe
  • Earth revolves around the sun in a circular path
• Ptolemaic universe


  • Earth was at the center of the universe, while the other celestial bodies revolved around the Earth in perfect circles with constant velocity
  • Planets revolved on epicycles (small spheres) which moved around the deferent (large sphere)
  • Stars belonged to the celestial sphere which was located beyond the planetary spheres
  • Earth was moved from its original position to a position below the center of the system that is still inside the deferent
• Copernicus' model


  • Revived the heliocentric model of Aristarchus
  • Sun was at the center of the universe
  • Order of planets from the sun is Mercury, Venus, Earth, Mars, Jupiter, Saturn and beyond the planets were fixed stars
• Tycho Brahe's model


  • Earth was at the center and the sun and the moon revolved around it, and all the other planets orbited the sun (Tychonic System)
• Motion


  A change in position with respect to a reference point and time
• Reference points are very important in describing the motion of objects
• Aristotle's view of motion

  • Motion did not only refer to locomotion or a change in position
  • He classified motion as: Terrestrial (or sub lunar) and Celestial
• Terrestrial motion


  The movement of objects on earth
• Elements according to Aristotle


  • Earth (center)
  • Water
  • Fire
  • Air
• Each element had a natural place
• When an element was removed from its natural place, it would return to its natural place following a straight line (rectilinear) motion
• Natural motion


  • If you pick up a small piece of rock and drop it, it would move toward earth where it really belongs
  • Why it rained? It rained because the sky was not the natural place of water. That was why the rain fell
• Violent (or unnatural) motion


  Lifting a rock is a violent motion because the rock was removed from its natural place
• Celestial motion


  The motion of celestial bodies which only possessed the tendency for uniform circular motion
• Hipparchus of Nicaea (190 BCE-120 BCE) was able to determine correctly the circumference of Earth
• Hipparchus was once considered as the greatest observational astronomer because he was able to explain the precession of equinoxes
• Precession of Equinoxes


  The movement of the Earth relative to its orbital plane
• Copernicus's view of motion

  • He had two descriptions of Earth's motion based on his observations (rotation and revolution) which are classified as either diurnal (daily) motion or annual (yearly) motion
  • Diurnal Motion refers to the rotation of earth about its axis from west to east
  • Annual Motion refers to the movement of earth in reference to the sun
• As the Earth rotates, some of its parts are exposed to the sun's rays while other parts are not, resulting in the occurrence of day and night
• Earth revolves around the sun from west to east, taking around 365 ¼ days (365 days and 6 hours) to be completed and is the reference for the number of days in a standard year
• The occurrence of seasons (spring, summer, autumn, and winter) is a consequence of both earth's revolution and tilted axis
• Isaac Newton


  English mathematician, physicist, astronomer, theologian, and author who is widely recognized as one of the most influential scientists of all time, and a key figure in the scientific revolution
• Principia Mathematica


  Book written by Isaac Newton where he formulated the laws of motion and universal gravitation that formed the dominant scientific viewpoint until it was superseded by the theory of relativity
• While most people know what Newton's laws say, many people do not know what they mean (or simply do not believe what they mean)
• 1st Law (Law of Inertia)

  An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force
• Inertia


  • The tendency of an object to resist changes in its velocity: whether in motion or motionless
• Objects in motion slowing down and becoming motionless


  • Friction
• Types of friction


  • Sliding friction
  • Rolling friction
  • Fluid friction (air or liquid)
  • Static friction
• When a book is slid across a table


  It comes to rest due to the force of friction
• In the absence of a force of friction, the book would continue in motion with the same speed and direction - forever! (Or at least to the end of the table top)
• Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 m/hour
• 2nd Law (Law of Acceleration)

  Force equals mass times acceleration (F=ma)