We now understand that the earth rotates around its axis one complete rotation e
ID: 1522750 • Letter: W
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We now understand that the earth rotates around its axis one complete rotation every 24 hours, but how would you prove that? I could argue with you that the sky is rotating and the earth is fixed. Historically, the first experiment to prove this was called a Foucault Pendulum after French physicist Leon Foucault. The pendulum consisted of a 28 kilogram brass-coated lead bob at the end of a 67 meters long thin wire that he hung from the ceiling of the Paris Observatory. Since the angular momentum of a swinging pendulum is constant, as the Earth rotates relative to the stars, the swinging bob does not. This made the pendulum "appear to rotate" around the room as it swung. This is just historical context for the following question. Let's say I wanted to repeat this experiment with a long solid rod that had the same oscillation period as Foucault's original pendulum, and that I wanted to hang that pendulum form the 3_rd floor ceiling in the SSC atrium. If the atrium is 20 meters below that point, will my new toy pendulum fit?Explanation / Answer
In a non-rotating earth, the motion of a pendulum is confined in one vertical plane only. But because of the rotation of the earth, the plane of motion of the pendulum is no longer stationary. With the earth rotating, let us say counter clockwise, underneath the oscillating pendulum, the vertical plane of motion of the pendulum wll appear to rotate in the opposite direction, namely clockwise. A pendulum that moves in this way is called Foucault pendulum named after the man who first made the demonstration that it actually occurs.The laws of conservation of angular momentum predict that The Earth must rotate to preserve its orbit around the The Sun, if it did not we would be pulled into The Sun by its gravity. Along with this the pattern of night and day suggest The Earth spins on its axis. We see the stars rotating in the sky, if they were orbiting the earth, they are all different distances so they would all be orbiting in different periods. The nearest star is 4 light years away, if it were orbiting earth it wouls have to travel 4ly x 2 x Pi which is about 25 light years per day at a speed of 9000 times faster than the speed of light which we know is impossible.
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