Artificial Satellites

To understand how a satellite goes into orbit, imagine yourself throwing a rock from the peak of a high mountain. While the rock travels away from you, gravity constantly pulls it down, and it finally hits the ground.

Suppose that you are powerful enough to throw it halfway around the world. Gravity still acts on the stone, preventing it from flying off into space. It follows a curved path until it hits the Earth's surface.

To go into orbit, the stone would have to travel very fast indeed at about 29.000 kph if it were 100 km in altitiude. Gravity would still try to pull it down, but at that speed the outward pull of centrifugal force balances the gravitational pull.

National standards (9-12) addressed

National standards (5-8) addressed

For better understanding of the artificial satellite we will conduct a simple experiment:

Materials needed

  • Some plasticine
  • A small, thin plastic tube
  • Some fishing line
  • And two paperclips Instructional goal:

    To demonstrate the orbit of an artificial satellite.

    Step 1
    Split the plasticine into two pieces, one five times heavier than the other.

    Step 2
    Thread the line through the thin plastic tube. Tie paperclips to each end, and push one clip into each ball of plasticine. Holding the plastic tube upright with the small ball on the top. Swing the tube fast in a circle.

    Picture 1

    Step 3
    The small ball will swing out, pulling the big ball up. The outward pull of the small ball is its centrifugal force. For a satellite, this must exactly balance gravity if it is to stay in orbit.

    Picture 2

    Step 4
    Hold the tube steady. As the small ball slows down, its centrifugal force is reduced and it moves back towards the tube like a satellite slowed by atmospheric friction spiraling out of orbit.

    Picture 3


    We have three orbits that a satellite can attain. One is the orbit where the satellite will go in circles, second the satellite will go in ellipses and the third where the satellite will live the orbit. To better understand the motion of the satellite we will have to visit Newton's second law:


    Where "v" is the linear speed of the satellite, "R" the radius of the planet, "M" is the mass of the planet and "m" the mass of the artificial satellite.


    From the last formula combined with this one we will get the "first space speed", and the orbit will be circular:

    Orbit 1

    But if the speed of the artificial satellite increases, the satellite will go faster than the first space speed and slower than the second space speed, and the object will get an elliptical orbit.

    Orbit 2.

    By increasing the speed faster than the second space speed the satellite will live the orbit.


    Author: Vladimir Simonovski