SSP 1

The pressure is not constant throughout a planetary atmosphere. A balance (equilibrium) is maintained between the outward pressure force and the inward gravitational force.

• 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.

True

• 1. The stars moved around a fixed Earth.
• 2. Could not explain retrofrad motion or phases of Venus.

P(h)=Psexp(-µmHgh)/kT

• 1. Planets, including Earth, orbit the Sun.
• 2. Phases of Venus and retrograd motion coud be explained in this model.

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.

F=Gm₁m₂/r²

• 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.

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

• 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.

• 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.

v=√2GM/r