Most of the time, the relative motion of the earth does not affect our perception of motion. Since everything is moving, there is no fixed reference point against which the motion of things can be described. All motion is relative to whatever point or object we choose. Thus, a parked bus has no motion with reference to the earth's surface; but since the earth spins on its axis, the bus is moving about 1,000 miles per hour around the center of the earth.
There is no point in space that can serve as a reference for what is actually moving. However, in 1848, Jean Foucault discovered that when a large pendulum swings, the earth appears to "move under it."
To prepare for this article, every one should understand that everything in the universe exerts gravitational forces on everything else, although the effects are readily noticeable only when at least one very large mass is involved (such as a star or planet). Gravity is the force behind the fall of rain, the power of rivers, the pulse of tides; it pulls the matter of planets and stars toward their centers to form spheres, holds planets in orbit, and gathers cosmic dust together to form stars. Gravitational forces are thought of as involving a gravitational field that affects space around any mass. The strength of the field around an object is proportional to its mass and diminishes with distance from its center. For example, the earth's pull on an individual will depend on whether the person is, say, on the beach or far out in space.
Changes in motion—speeding up, slowing down, changing direction—are due to the effects of forces. Any object maintains a constant speed and direction of motion unless an unbalanced outside force acts on it.
Everyone especially students should begin to understand how the principle of universal gravitation explains the architecture of the universe and much that happens on the earth. The principle will become familiar from many different examples (star formation, tides, comet orbits, etc.) and from the study of the history leading to this unification of earth and sky.
It is important for all to escape the common misconceptions that the earth's gravity does not extend beyond its atmosphere or that it is caused by the atmosphere.
Some usefull FAQ's for you
What is the orgin of word "PENDULUM"?
Word comes from LATIN word "pendulus" which mean "hanging"
What is the purpose of use Pendulum?
To understand how the motion of the Foucault pendulum proves that the earth is rotating.
Related Videos of Pendulum
This is a video compilation of a Foucault pendulum in action at the Houston Museum of Natural Science. The rotation of the plane of the pendulum's oscillations demonstrates that the earth is a rotating reference frame. The number of rotations it makes in one day (about 180 degrees in 24 hours) also indicates the latitude of the museum (about 30 degrees north of the equator).
By my count, there must be exactly 144 pins forming a circle on the floor underneath the pendulum. In the video, you will see two pins get knocked over, 1 hour apart. There was another pin between these two that gets tipped over, but this event is not on the video.
With this data, I expect the time for two adjacent pins to get knocked over to be 48/144 = 0.33 hours. Between the 3 pins getting knocked over, it should have taken only 40 minutes, not 1 hour. Perhaps the spacing or position of the pins were uneven?
At latitude L in the northern hemisphere, the plane of the pendulum's oscillations rotates clockwise by the amount 360*sin(L) degrees in one day. One can google to find out how this expression can be obtained, but let me point out two illuminating remarks regarding this expression: (1) It is the projection of the angular velocity of the earth (magnitude 360 degrees per day) onto the vertical direction at latitude L. (2) It is related to the net rotation of a vector resulting from parallel transport along a closed circuit on the surface of a sphere. This rotation is given by the solid angle subtended by the surface enclosed by the circuit. In the case of our pendulum, the circuit is the circle of latitude. We get 360*sin(L) after subtracting 360 from the solid angle subtended by the surface enclosed by the circle of latitude and that includes the north pole.
The museum is at latitude 29 deg 46 min N, according to the touch-screen panel near the pendulum. My old Magellan handheld GPS reported coordinates of 29 deg 43.281 N, 95 deg 23.353 W, 23 ft, which is pretty close. Plugging L~30 deg into our formula, we get 360*sin(30)=180 deg/day.
Other facts I learned from the touch-screen:
Pendulum weight - 180 lbs (81.6 kg)
Length - 61.6 feet (18.8 m)
Period - 8.71 sec
Swing angle - 5 deg
Displacement - 65 inches (1.65m)
This Foucault pendulum was invented by Jean Bernard Léon Foucault was a French physicist also known as Shortly "Léon Foucault".
Click here to read more about Léon Foucault and his inventions
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