Topic 7

Cards (20)

  • Weight
    W = mg, Weight (Newtons, N) = mass (kilograms, kg) x acceleration due to gravity (metres per second, m/s)
  • The greater the value of g

    The greater the weight of the object
  • The greater the mass of the planet

    The greater value of g on that planet
  • Our Solar System consists of
    • The Sun
    • Eight planets that orbit the sun
    • Natural satellites orbit the planets (e.g. the Moon for Earth)
    • Dwarf planets orbit the sun (including Pluto, Ceres)
    • Asteroids and comets
  • Planets in our Solar System
    • Mercury
    • Venus
    • Earth
    • Mars
    • Jupiter
    • Saturn
    • Uranus
    • Neptune
  • Planets
    • Smaller planets are made of primarily rock, then the larger planets are primarily gas
    • All planets orbit the Sun on the same plane
    • All planets rotate, just at different speeds
    • Some planets rotate in the opposite direction or on a skewed axis to the other planets, and this may be due to past collisions throwing its axis off balance
    • Larger planets have rings, as their gravitational field is so strong it attracts debris
  • Geocentric model

    Initial model suggested Earth was at the centre, the planets, our moon, and the sun, orbited the Earth
  • Heliocentric model

    Model with the sun at the centre
  • Evidence for heliocentric model
    • Mars' "retrograde motion"
    • Galileo observing moons orbiting Jupiter
    • Kepler showed that the planets orbited in ellipses, and not circles
  • Planetary Orbits
    1. Gravitational force causes the planet to change direction constantly (it moves in a circle around the sun)
    2. Speed of the planet is constant
    3. Velocity is always changing
    4. Force causes the planet to accelerate without increasing its speed
  • If the planet moves closer to the sun (orbital radius decreases)

    Gravitational attraction to the sun increases, so the orbital speed of the planet increases
  • Red Shift
    Light appears red shifted from galaxies which are moving away from Earth
  • The red shift increases as the distance away from the earth increases which is evidence of an expanding universe
  • Cosmic Microwave Background (CMB) radiation

    When the universe was very young, everything, the first stars and rock, would be very hot, and should have emitted lots of short-wavelength radiation. This radiation, as the universe expanded over time, would have been stretched to become microwaves. This background radiation is present wherever you point a telescope in the sky.
  • The big bang accounts for all the experimental evidence, so it is the most accepted model currently
  • Steady State Theory
    As universe expands, matter is constantly being created so there is a constant density of matter in the universe. However, this theory does not account for CMB and is not correct as the universe has evolved and not stayed the same.
  • Life Cycle of Star
    1. Dust and gas cloud is present in a galaxy
    2. Interstellar matter clump together to form clouds called nebulae
    3. Gravitational attraction between the gas/dust particles draws them together
    4. Cloud becomes more concentrated, as the particles get closer
    5. Temperature and pressure of the cloud increases
    6. Fusion occurs as the light (mainly hydrogen gas) nuclei fuse together to form helium nuclei
    7. Eventually the star runs out of gas to fuse, and collapses if massive (supernova, neutron star or black hole) or swells to a red giant and then contracts to a white dwarf if normal-sized
  • Observing the Universe
    • Observations can use any wavelength in the EM spectrum
    • Telescopes outside the atmosphere are needed to measure X rays, Gamma, UV as the atmosphere does not allow these to reach the ground
    • Early refracting telescopes evolved to reflecting telescopes, which could be made larger and cheaper
    • Technological advances allowed other parts of the EM spectrum to also be measured and collected
  • How is a main sequence star stable
    the outward force from fusion is equal to the inwards gravity force
  • How does a nebula turn into a main sequence star
    gravity causes the nebula to collapse causing the temperature to increase and fusion begin