orbital motion

• Circular orbit


  Path of a circle followed by a planet orbiting the Sun
• Elliptical orbit


  More accurate path followed by planets orbiting the Sun, not perfectly circular
• The Earth's orbit is virtually circular
• Force of gravity


  Holds planets in their orbits around the Sun
• Natural satellite


  The Moon orbiting the Earth
• Artificial satellite


  Man-made satellites orbiting the Earth, e.g. for satellite TV
• Geostationary satellite


  Orbits the Earth once every 24 hours, always pointing to the same part of the Earth
• For circular orbits, the force of gravity


  Changes the velocity but not the speed of the orbiting object
• If the speed of a satellite changes


  The radius of its orbit must also change to maintain a stable orbit
• This is also true for planets and moons orbiting the Sun and Earth respectively