Einstein's Universe exam #1

• Geocentric Model - Ancient perspective 

  • Earth, immovable, is surrounded by crystalline spheres which hold the sun, moon, and planets 
  • All stars are fixed on an outer sphere 
  • Consistent with Aristotle's law of motion
• Aristotle’s laws of motion 

  • Objects are naturally at rest 
  • Objects move to rest
  • Forces are needed to keep an object in motion
  • Heavy objects fall faster than lighter ones 
•  Problems with geocentrism

  1. planets with varying brightness 2. retrograde motion
• Retrograde Motion: When Earth is circling the sun in a smaller orbit than another planet and we pass that planet, the planet will appear to be moving backward
• epicycles: a small orbit that moves along a much larger orbit
• Heliocentric model: planets orbit the sun, sun as the center of the universe
• Keplers laws:

  1. Law of orbits: planetary orbits are ellipses, not circles, with the sun at one of the foci 
  2. Law of areas: planets sweep equal areas in equal times 
  3. Law of periods
• problems with heliocentricism

  1. no stellar parallaxes
  2. vertical motion in a straight line would be impossible
• Galileo and Heliocentrism: Galileo's observations of phases of Venus proves that it orbits the sun and not earth
• • Galileo's law of motion 
  • Uniform motion is natural 
  • Forces can change motion
• A coordinate system allows us to precisely describe and objects position in space
• kinematics: a way to describe an objects motion and how it changes with time
• On a coordinate system, positive number are to the right of the origin and negative numbers are to the left
• Origin: define the “zero point” of the coordinates can be anywhere you choose 

  Time (t): the progression of existence, measure in seconds (s)

  Position (x): the coordinates of an object relative to the origin, measured in meters (m)

  Displacement (Δx) - the difference between two positions, also measured in meters (m)
• Position plot: Two dimensional diagram describing the position of an object
• Velocity (V): how fast something is moving in a particular direction
• Speed = how fast something is moving 

  Velocity = how fast something is moving in a particular direction
• Acceleration = How fast the velocity changes in a particular direction.
• Newtons 1st law: Bodies in motion tend to stay in motion, bodies at rest tend to stay at rest
• Newton's 2nd law: Forces change motion
• Newton's 3rd law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body
• Universal law of gravity: any abject in the universe attract any other object
• Conservation of Mass: The mass of a system of particles does not change.
• Conservation of Energy: The total energy of a closed system of particles does not change.
• Energy = “the amount of motion or the capacity to cause motion” 
• Kinetic energy = energy of motion
• Potential energy = potential to move or cause motion
• Radiation = energy transmitted away from the source
• An inertial reference frame is a frame moving at constant velocity with respect to to another inertial reference frame
• “aberration of starlight”:  to measure the speed of light.
• A wave is a disturbance of the medium that propagates, transporting energy.
• Longitudinal (sound): propagation and disturbance in the same direction
• Transverse  (string):  propagation and disturbance in perpendicular directions
• CONSTRUCTIVE interference: the waves add together to make a single bigger wave
• DESTRUCTIVE interference: waves cancel each other and the wave goes away.
• Black body: An opaque body that absorbs all incident light regardless of its wavelength
• a black body at room temp: peak emission is in infrared (appears black)

  a black body at hotter temp: glows in visible light
• Temperature: measures an object's internal energy
• Heat: the transfer of internal energy

  • hot  - when internal energy transfers to you 
  • Cold - when it transfers from you
• The ultraviolet catastrophe

  • The wave theory of light predicted 

  1. All waves have the same energy regardless of their wavelengths 
  2. The number of short wavelength (high frequency) 

  waves increase very fast

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