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  1. Explain Hydrostatic Equilibrium
    The pressure is not constant throughout a planetary atmosphere. A balance (equilibrium) is maintained between the outward pressure force and the inward gravitational force.Image Upload 1
  2. General facts about Sun
    • 1. It's a star, a ball of (mainly) Hydrogen gas.
    • 2. 700,000 km in radius.
    • 3. Generates heat and light through nuclear fusion.
    • 4. Surface temp. 5800K, central temp. 15 million K.
    • 5. Hydrostatic equilibrium maintained between pressure and gravity.
  3. T or F: The orbits of the planets are elipses and lie in, or close to the eciptic plane.
  4. Describe the problems with the Geocentric model of the universe
    • 1. The stars moved around a fixed Earth.
    • 2. Could not explain retrofrad motion or phases of Venus.
  5. Hydrostatic Equilibrium equation?
  6. Describe the Heliocentric model of the universe
    • 1. Planets, including Earth, orbit the Sun.
    • 2. Phases of Venus and retrograd motion coud be explained in this model.
  7. State Newton's Univeral Law of Gravitation
    Gravity is a force of attraction between all matter in the universe causing apples to fall from trees and the Moon to orbit the Earth.

  8. Describe retrograd motion
    • 1. Retrograde motion is when a planet appears to be moving backwards in it's orbit.
    • 2. Copernicus reasoned that planets further away from the sun would move more slowly than closer ones. As a faster planet overtakes the Earth in their rotations, its motion against the stars, as seen from the Earth, reverses.
  9. What is g=GM/R2?
    The gravitational field at the planets surface.

    For Earth, g=6.673*10-11 x 5.974*1024/(6.378*106)2

    So g=9.80ms-2
  10. What can be determined from the following formula:

    • 1. If two planets have the same density, the larger will have the higher surface gravity.
    • 2. If two planets have the same radius, the denser planet will have the higher surface gravity.
  11. Explain escape velocity
    • 1. If a projectile is launched vertically upwards as the projectile climbs, the planets gravity slows it down. It's kinetic energy is converted to potential energy.
    • 2. For an object to escape, the kinetic energy must equal potential energy.

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