The Universe

• What does our solar system consist of?

  The sun, 8 Planets, natural satellites, Dwarf planets, Comets and asteroids
• What did Ptolemy suggest about the universe?

  That the earth was the centre
• What did Copernicus suggest about the universe?

  That the sun is at the centre and the planets and the orbit it.
• What did Galileo contribute theories about the universe?

  He used telescopes to support Copernicus’ suggestions about the sun, and suggested that moons orbit planets.
• Describe the orbit of moons, planets, comets and artificial satellites

  They orbit in an elliptical shape
• Why, at stable orbit, does the speed change?

  At higher speeds, the object requires a greater centripetal force. For a greater centripetal forces, the gravitational force must increase. This is achieved by the radius of the orbit being reduced.
• Explain how the force of gravity acting on a satellite affects its speed and velocity

  The force can alter its velocity since the direction is continually changing, it can’t cause a change of speed since there is no force component in the direction of motion.
• Comet

  mostly ice and dust, large elliptical orbits
• Asteroids

  Mostly in the asteroid belt between Mars and Jupiter, mostly rock and metal.
• Galaxies

  Collections of billions of stars, held together by gravity, orbiting around the centre
• An orbit

  A curved path of one celestial object or spacecraft, around another celestial body
• Instantaneous velocity 


  Momentum of a satellite, it’s direction of velocity
• Why do smaller orbits lead objects to travel faster?

  More momentum, from higher speed, is required to combat the higher gravitational pull