the solar system

• The Sun


  Our nearest star, relatively small when compared to other stars in the universe
• Solar System


  Contains the Sun and everything that orbits it
• Milky Way


  A galaxy close to our Solar System, containing billions of stars
• Planets


  Eight planets in the Solar System, orbiting the Sun at different distances
• Planets


  • As distance from the Sun increases: temperature decreases, time taken to orbit the Sun increases
  • A planet must have enough gravity to be round and clear its neighbourhood of other objects
• Moons


  Natural satellites that orbit planets
• Dwarf planets


  Objects orbiting the Sun that are massive enough to be rounded by their own gravity but have not cleared their neighbourhood
• Asteroids


  Smaller objects orbiting the Sun in highly elliptical orbits, made of metals and rocky material
• Comets


  Small objects made of rocky material, dust and ice that produce a distinctive tail as they approach the Sun and vaporise
• The Sun is our nearest star
• The Sun is a relatively small star when compared to other stars in the universe
• Our Solar System contains the Sun and everything that orbits it
• The Solar System was formed around 4.6 billion years ago from a large cloud of dust and gas, called a nebula
• Formation of the Solar System

  1. Nebula collapsed under its own gravity

  2. Transferred gravitational potential energy to kinetic energy in particles

  3. Nebula became denser and rotated more rapidly

  4. Collisions between particles caused kinetic energy to be transferred as internal energy and thermal energy

  5. Core of the nebula began to form a hot, dense protostar
• When the Sun's core became hot enough and dense enough, nuclear fusion reactions began
• Nuclear fusion


  The joining together of two smaller atomic nuclei to produce a larger nucleus. Radiation is released when this happens. Nuclear fusion happens in stars like our Sun, and in hydrogen bombs.
• A star like the Sun is at equilibrium - gravity tends to pull it inwards, and radiation pressure from the nuclear reactions tends to expand it outwards
• The Sun is our nearest star. It is a relatively small star when compared to other stars in the universe
• Our Solar System contains the Sun and everything that orbits it
• Orbital motion


  Gravity provides the force needed to maintain stable orbit of both planets around a star and also of moons and artificial satellites around a planet
• Explaining orbits


  1. If the satellite is moving too quickly then the gravitational attraction between the Earth and the satellite is too weak to keep it in orbit, and the satellite will move off into space (occurs at speeds around or above 11,200 m/s)

  2. If the satellite is moving too slowly then the gravitational attraction will be too strong, and the satellite will fall towards the Earth (occurs at speeds below 7600 m/s)

  3. A stable orbit is one in which the satellite's speed is just right - it will not move off into space or spiral into the Earth, but will travel around a fixed path
• The Sun is our nearest star. It is a relatively small star when compared to other stars in the universe
• Our Solar System contains the Sun and everything that orbits it
• Polymers


  Molecules made from a large number of monomers joined together in a chain
• Enzymes


  • They increase the rate of chemical reactions without themselves being consumed or permanently altered by the reaction
  • They increase reaction rates without altering the chemical equilibrium between reactants and products
• As temperature increases


  The rate of reaction increases
• Orbits and constant speed

  When an object moves in a circle at a constant speed, its direction constantly changes. A change in direction causes a change in velocity, as velocity is a vector quantity - it has an associated direction as well as a magnitude. A change in velocity results in acceleration, so an object moving in a circle is accelerating even though its speed may be constant.
• Centripetal force


  Force, needed for circular motion, which acts towards the centre of a circle. Gravitational attraction provides the centripetal force needed to keep planets and all types of satellite in orbit.
• Gravitational attraction between two objects

  Decreases with distance. The closer the two objects are to each other, the stronger the force of gravity between them. If the force between them is greater, a greater acceleration will occur. The greater the acceleration, the greater the change in velocity - this causes the object to move faster.
• Objects in small orbits travel faster than objects in large orbits
• Polar orbits


  Satellites travel over the Earth's poles. They travel very close to the Earth (as low as 200 km above sea level), so they must travel at very high speeds (nearly 8,000 m/s).
• Geostationary orbits


  Satellites take 24 hours to orbit the Earth, so the satellite appears to remain in the same part of the sky when viewed from the ground. These orbits are much higher than polar orbits (typically 36,000 km) so the satellites travel more slowly (around 3 km/s).