physics p2

• Electromagnetic waves


  Transverse waves
• Satellite


  Anything that orbits a planet
• Types of satellites


  • Natural
  • Artificial
• Natural satellite


  Not man-made
• Planets in the solar system

  • Mercury
  • Venus
  • Earth
  • Mars
  • Jupiter
  • Saturn
  • Uranus
  • Neptune
• Orbit of planets


  • Slightly elliptical, not a perfect circle
• Other structures in the solar system

  • Asteroids
  • Comets
• Asteroids


  Mostly made of rock and metal, found in the asteroid belt between Mars and Jupiter
• Comets


  Mostly made of ice and dust, have very elliptical orbits and travel to the outskirts of the solar system
• Galaxy


  Massive collection of billions of stars, most with their own solar systems
• Milky Way galaxy


  The galaxy that our solar system is a part of
• Gravity


  • Holds stars together in galaxies, causing them to spin around the middle
• Universe


  Vast expanse of mostly empty space, scattered with galaxies
• The universe is mostly empty space with unimaginable distances between adjacent galaxies
• Solar systems consist of a central star orbited by planets, which can be orbited by satellites
• Orbit


  The curved path of one celestial object or spacecraft around another celestial object
• Objects orbit rather than flying off in a straight line or being pulled in towards the object they're spinning around
• Newton's first law


  An object traveling at a certain velocity will continue to travel at that velocity unless acted upon by a resultant force
• The moon is traveling at 1023 m/s


  It should continue to travel in this direction and at this speed forever
• The earth is massive and relatively close to the moon

  It exerts a strong gravitational pull which is felt as an attractive force towards the earth
• The moon has a lot of momentum in its forward direction


  The gravitational force isn't strong enough to completely pull it in towards the earth
• The earth is always applying a gravitational force on the moon


  It's always changing the moon's direction
• Orbiting


  The moon is basically always orbiting around the earth
• The moon's speed is always the same


  Its velocity is constantly changing
• Acceleration


  Any change in velocity means an acceleration
• Every time the moon changes direction as it orbits, it's actually accelerating even though it's not getting any faster or slower
• Steady orbit


  • Instantaneous velocity of orbiting object
  • Gravitational pull of larger object
• If the moon's orbit is pulled inwards so it's closer to the earth


  The size of the gravitational force will be much greater
• To avoid being sucked in towards the earth

  The moon would have to start traveling much faster to maintain a stable orbit
• The smaller an object's orbit, the faster that object must be traveling in order to maintain a stable orbit
• Redshift


  The phenomenon where the light from distant galaxies appears shifted towards the red end of the spectrum
• Big Bang


  The theory that the universe began in a tiny, extremely dense and hot state, and has been expanding and cooling ever since
• From Earth, every direction we look into space, the galaxies seem to be moving further and further away from us, or in other words, the universe is expanding
• Evidence for the expanding universe

  • The redshifting of light from distant galaxies
• Absorption spectra


  1. Certain wavelengths of light are absorbed by chemicals in the sun's atmosphere

  2. This results in a pattern of dark lines in the spectrum observed on Earth
• Life cycle of stars

  1. Big cloud of dust and gas (nebula)

  2. Gravity pulls dust and gas together to form a protostar

  3. Protostar gets bigger and denser

  4. Temperature and pressure increase

  5. Hydrogen nuclei fuse to form helium (nuclear fusion)

  6. Star becomes a main sequence star

  7. Main sequence star has balanced outward and inward pressure

  8. Star runs out of hydrogen

  9. Gravity contracts star

  10. Nuclear fusion forms heavier elements up to iron
• Main sequence star


  • Long stable period that can last for billions of years
  • Outward pressure from nuclear fusion balanced by inward pressure from gravity
• Red giant


  1. Expels outer layers

  2. Leaves behind a hot dense solid core (white dwarf)

  3. White dwarf cools to become a black dwarf
• Red supergiant


  1. Undergoes more nuclear fusion

  2. Eventually explodes in a supernova

  3. Condenses into a neutron star (if big)

  4. Condenses into a black hole (if very massive)
• Supernovas eject heavy elements across the universe