Imagine that you could climb an imaginary mountain whose summit pokes above the Earth's atmosphere (It would be about ten times higher than Mt. Everest). If you threw a baseball from the mountain top, it would fall to the ground in a curving path. Two motions act on it: trying to go in a straight line and falling toward Earth. The faster you throw the ball, the farther it will go before it hits the ground.

If you could throw the ball at a speed of 17,000 mph, it would never reach the ground. It would circle the Earth in a curved path, otherwise known as orbit. (It would be traveling at 5 miles per second and take about ten minutes to cross the United States.) This is the speed needed to put satellites into orbit, which is why the Space Shuttle and other satellites have such powerful boosters.

You can't approach that speed, but you can start to see how increasing force influences distance traveled.

Measure the trajectory of a classroom satellite.

  1. Roll a marble or a small ball off the edge of a table.
  2. Have someone mark with chalk where the marble or ball leaves the table and where it first hits the floor. The curved path between these two points is its trajectory.
  3. Repeat the process using greater force each time. Measure the distance between the chalk marks on the floor which mark where the marble landed each time. How did its trajectory (its curved path after it leaves the table) change?
  4. Cut out a circular piece of paper and put it on top of the record player turn table.
  5. Turn on the record player and have someone draw a straight line with a marker on the paper as the turntable is turning.
  6. Turn off the record player and see what the line looks like.

Why is it curved? (record player was turning)

How is this like a satellite circling Earth? (satellite attempts to follow a straight line but is pulled inward by gravity).

  1. Could you break out of Earth's orbit by going faster?

What happens when you try to draw a line on the rotating turntable more rapidly?


  • marble or small ball
  • chalk
  • record player, circular pieces of paper to fit onto record player, turntable, marker