185 1 year, French physicist Jean Foucault placed a pendulum device in the national funeral home in Paris. The length of the pendulum is 67 meters. The pendulum at the bottom is an iron ball weighing 28 kilograms, and a slender needle is embedded under the iron ball. What is this huge device used for? Foucault was trying to prove the rotation of the earth. He imagined that when the pendulum swings, it will keep a fixed swing direction without external force. If the earth is spinning, the ground under the pendulum will also rotate, while the pendulum hanging in the air tends to keep its original swing direction. For the observer, the swing direction of the pendulum will change relative to the ground. The principle is figured out, but the experiment is not easy to do. Because the change of swing direction is subtle, a slightly stronger airflow will change the experimental results. Because the longer the swing arm, the more obvious the experimental effect, so in order to observe the change of direction, the experimental site must be set in the hall with high ceiling to hang the pendulum. Foucault finally chose the towering national funeral home in Paris as the experimental site, and placed a sand table under the pendulum. When swinging, the swing tip will mark the sand table to record the swing direction.

The experimental results are completely consistent with Foucault's idea, and the pendulum swings slowly and continuously from east to west. Foucault's demonstration directly proves the rotation of the earth from west to east, so people call the pendulum in the experiment "Foucault pendulum". At that time, the French government also awarded Foucault the Fifth Order of Honorary Knight in recognition of his scientific contributions. Foucault's experiment triggered an experimental upsurge all over the world, and people everywhere followed Foucault's example and revealed the rotation of the earth with a long pendulum. It is found that at the poles of the earth, the pendulum plane of Foucault pendulum rotates once every 24 hours, while at the equator, Foucault pendulum does not rotate in any direction. In the region between the poles and the equator, the rotating speed direction of Foucault pendulum is between the two.

The earth rotates once every 24 hours. Because the circumference of the equator is about 40,000 kilometers, people have the saying that "sitting on the ground, traveling 80,000 miles a day". At a point on the equator, the speed is close to 500 meters per second, which is the speed when the bullet leaves the chamber. We fly like bullets, but we don't feel anything, because under the action of inertia, all the objects around us follow the earth at high speed, but they are inseparable from each other. We don't know the true face of the earth, because we are in this mountain.

As mentioned earlier, the rotation speed of Foucault pendulum in different parts of the earth is different, which shows that the linear speed in different parts of the earth's surface is different. Therefore, Foucault pendulum can not only verify the rotation of the earth, but also be used to find the latitude of the pendulum.

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185 1 year, a pendulum designed by French physicist Foucault to prove the rotation of the earth is called the boko pendulum. Foucault pendulum rope is 67 meters long, and the pendulum at the end of the rope weighs 27 kilograms. This pendulum swings freely for a long time, which is convenient for people to observe. There is a graduated disk under the pendulum, and a straight line passing through the center of the circle is engraved on the disk. At rest, the center of the pendulum should be aligned with the center of the disc. When observing, first make sure that a straight line in the disk coincides with the meridian passing through the center, and then push the pendulum to rotate along the north-south direction of the meridian. After a while, you will see that the swing direction deviates from the warp direction. Deflection to the right in the northern hemisphere, the longer the time, the greater the deflection angle. After the pendulum starts to move, it is not affected by other forces except gravity. According to the law of inertia, the direction of the pendulum should remain the same. But the pendulum was deflected. This is because of the rotation of the earth. Standing on the earth, we don't feel that the direction of the meridian is changing, but we feel that it is deflecting. If Foucault is placed in the north pole, with the north pole at the center of the disk, it takes 24 hours to make one revolution, with an hourly deflection of 15. If the pendulum is located at the equator, it will not deviate; If the pendulum is placed at any latitude between the equator and the poles, the deflection angular velocity (θ) of the pendulum plane is directly proportional to the sine function of latitude (φ). That is θ = t sin φ. T is the angle at which the earth rotates every hour. In the southern hemisphere, the pendulum leans to the left.