The Universe

• Why does your weight vary across planets?

  Your weight is dependant on g, since weight = mass x g. The gravitational field strength (g) of a planet varies depending on the size of the planet. This means that your weight will also vary.
• What is gravitational field strength?

  Approximately 10 M/Kg.
• What does our solar system consist of?

  -The sun (our star).

  -8 planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune).

  -The planet's natural satellites (i.e. the moon).

  -Dwarf planets.

  -Comets and asteroids.
• Name the planets in order, starting with the closest to the sun.

  Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
• What did Ptolemy suggest about the universe?

  That the Earth was at the centre.
• What did Copernicus suggest about the universe?

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

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

  They orbit in an elliptical shape.
• Explain why for a stable orbit, the radius of orbit must change if the speed changes.

  At higher speeds, the object requires a greater centripetal force. For a greater centripetal force, 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.