PHYSCI

• Early Greek Beliefs (500 B.C.)


  • Most Greeks believed the Earth was flat
• Pythagoras (6th century B.C.)


  • Proposed that the Earth was spherical
• Anaxagoras (500-430 B.C.)


  • Observed shadows during lunar eclipses, supporting the spherical Earth theory
• Arguments for a spherical Earth by Aristotle (4th century B.C.)


  • Observed the Earth's shadow during lunar eclipses was always round
  • Noted changes in star constellations depending on one's position on Earth
  • Ships disappearing hull-first over the horizon indicated a curved Earth
• Tychonic System (late 16th century)


  • Combined aspects of Copernican heliocentrism and Ptolemaic geocentrism
  • Earth at the center
  • Sun, Moon, and fixed stars orbit Earth
  • Five known planets orbit the Sun
• Galileo's Contributions (1609-1610)


  • Developed an advanced telescope
  • Wrote "The Starry Messenger" in 1610, detailing his discoveries
• Galileo's Discoveries


  • Observed craters and mountains on Earth's Moon, indicating a varied surface
  • Discovered four satellites of Jupiter
  • Noted spots on the Sun, challenging the idea of a perfect celestial body
  • Observed the phases of Venus, suggesting it orbited the Sun, not Earth
• Kepler's Laws of Planetary Motion


  • Law of Orbits: Planets move in elliptical orbits with the Sun at one focus
  • Law of Areas: A planet covers the same area in the same amount of time, regardless of its position in orbit
  • Law of Harmonies: The square of a planet's orbital period is proportional to the cube of its average distance from the Sun
• Astronomical Phenomena Known Before Telescopes


  • Observed the motion of stars, the phases of the Moon, and the visibility of planets (Mercury, Venus, Mars, Jupiter, Saturn)
  • Used gnomon and sundials to track the Sun's motion
  • Observed lunar eclipses (Earth casting a shadow on the Moon) and solar eclipses (Moon blocking the Sun)
• Earlier Geocentric Views


  • Thales and Anaximander suggested the Earth was a disk or a cylinder
  • Comets were often regarded as omens of disaster
  • Observed changing paths and appearances of the Moon, basis for ancient calendars
  • Stars appeared to rotate around an axis, with variations in constellations depending on the time of year
• Aristotelian View of Motion


  • Motion was classified as natural or violent
  • Natural motion: Objects move according to their material or composition
  • Violent motion: Requires an external force to maintain motion
• Galilean View of Motion


  • Motion can be explained mathematically, independent of the object's composition
  • Horizontal motion: An object in motion continues to move unless acted upon by an external force
  • Vertical motion: Objects fall at the same rate regardless of their weight
• Newton's Laws of Motion


  • First Law (Inertia): An object at rest remains at rest, and an object in motion remains in motion unless acted on by an unbalanced force
  • Second Law (Force): The acceleration of an object depends on its mass and the amount of force applied
  • Third Law (Action & Reaction): For every action, there's an equal and opposite reaction
• Newton's Corpuscular Theory


  Light emitted by luminous objects consists of tiny particles of matter called "corpuscles" which travel in all directions with high velocity
• Huygens Wave Theory


  Light is a form of energy and travels as a wave, with each point of light acting as a source and sending waves in all directions
• Maxwell's Electromagnetic Theory


  Light is a wave made up of oscillating electric and magnetic fields that can move through space without requiring a medium
• Planck's Quantum Theory


  Light is propagated in the form of packets of energy called quanta or photons
• Propagation


  Electromagnetic waves traveling from one point or space to another, specifically when light waves travel through a medium
• Reflection


  When a ray of light approaches a smooth polished surface and the light ray bounces back
• Types of Reflection


  • Regular (specular) reflection: Parallel light rays strike a smooth and flat surface, resulting in reflected rays that remain parallel
  • Irregular (diffused) reflection: Parallel light rays hit a rough surface, causing the reflected rays to scatter in various directions
• Refraction


  The bending of light rays as they pass from one medium to another, due to a change in the speed of the light ray or wave
• Diffraction


  The slight bending of light as it passes around the edge of an object or a medium
• Types of Diffraction


  • Fraunhofer diffraction: Light waves diffract after passing through a narrow slit or aperture, producing a pattern of bright and dark fringes
  • Fresnel diffraction: Light waves diffract at an aperture or obstacle, and the waves spread out in various directions, interfering with each other
• Reflected light


  • Sunlight reflecting off the surface of a frosted window, causing the light to scatter in different directions due to the rough texture of the frosted glass
• Refraction


  The bending of light rays as they pass from one medium to another, thereby changing the path of the rays
• Refraction occurs due to a change in the speed of the light ray or wave
• Diffraction


  Slight bending of light as it passes around the edge of an object or a medium
• Types of diffraction


  • Fraunhofer diffraction
  • Fresnel diffraction
• Fraunhofer diffraction


  Occurs when light waves diffract after passing through a narrow slit or aperture, producing a pattern of bright and dark fringes. Observed in the far-field region, where the light waves are approximately parallel
• Fresnel diffraction


  Occurs when light waves diffract at an aperture or obstacle, and the waves spread out in various directions, interfering with each other. Observed in the near-field region, where the wavefronts are not approximately parallel
• Dispersion


  The separation or splitting of colors from its primary light ray, colors depending on its separated wavelength and frequency
• Chromatic dispersion is when the phase velocity of a wave varies on its frequency within a medium
• Dispersive medium is when waves of different frequencies travel at different velocities (through prism glass or known as dispersive prism)
• Humans have 3 color photoreceptors (red, green, blue) while a shrimp has 12, suggesting there may be undiscovered colors in the universe
• Interference


  Occurs when two or more light waves meet and combine, leading to constructive or destructive interference
• Constructive interference


  Waves align in phase, increasing overall light intensity and amplitude
• Destructive interference


  Waves are out of phase, decreasing light intensity or causing complete cancellation
• Thomas Young's double-slit experiment in 1801 demonstrated light's wave-like behavior through interference patterns
• Holography


  A method that captures and recreates the interference pattern created by the interaction of coherent light with an object
• A holographic recording contains comprehensive information about both the amplitude and phase of the light waves scattered by the object