Orbital Motion

• Natural satellites

  • The moon orbits the earth
• Artificial satellites

  • man-made
• What provides the force needed to keep a satellite in its orbit?

  • Gravity
• What does gravity do?

  • Allows planets, artificial and natural satellites to maintain their circular orbits.
• How do planets orbit?

  • They orbit the sun
  • The force of gravity holds the planets in their orbit
• Differences between natural(moon) and artificial satellites?

  • Moons are natural whereas an artificial satellite is man-made
• Explain why the velocity of the satellite changes as it orbits the Earth

  (3 marks).

  1. Force of gravity causes the satellite to accelerate to the Earth
  2. Acceleration causes a change in direction
  3. Velocity changes because the direction changes
• Similarities between moon and artificial satellites


  • Both orbit a planet
• Explain, in as much detail as you can, the scientific evidence for the “big bang” theory of the origin of the Universe.

  • Speed remains the same
  • Velocity changes as it constantly changes direction
• In a stable orbit, what would happen if the speed is changed?

  • The radius would change.
• How are radius and speed related in an orbit?

  • The greater the radius, the slower the speed.
• How can you keep an orbit stable when you change the radius?

  • Change the speed