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Directions to Making a Foucault Pendulum

In the winter of 1851, French physicist Léon Foucault came up with a simple and elegant way to prove to world that the Earth revolved around its axis in diurnal motion. He suspended a heavy round weight on a long cord from the ceiling of the Meridian Room in the Paris Observatory. He swung the weight in a straight line, and as time passed the swings rotated in response to the Earth's rotation. You can prove to your friends that the Earth revolves on an axis by making a Foucault pendulum of your own.

Things You'll Need

Room with a very high ceiling, at least 20 feet
Strong cord or rope, 25 feet
Medicine ball, 25 lbs.
Chair
Ladder

Instructions

- 1
  Take one end of your cord or rope, climb your ladder, and tie the cord firmly to the ceiling. You need to find a hook or a rafter or something sturdy enough to tie the rope to to support a 25-lb. weight in motion.
- 2
  Place the chair directly underneath the spot where you fixed the rope to the ceiling.
- 3
  Place the medicine ball on the chair and tie the rope around it, so that when you remove the chair the ball is suspended at the same height as the seat of the chair. You should have several feet of rope to work with, so wrap the rope several times around the ball to make a secure harness for it. Tie the rope very tightly into knots so that the rope does not move or come untied as the ball is in motion.
- 4
  Remove the chair so that the ball is suspended approximately 2 to 3 feet above the floor.
- 5
  Pull the ball back as far as you can and let it go so that it begins to swing in a straight line. After several minutes, you should be able to observe the line of the swing shift to the right if you are in the northern hemisphere.

Astronomy