Because the circumference of the equator of the earth is about 40 thousand kilometers, that is, 80 thousand miles, the earth rotates once, and it takes 80 thousand miles to sit on the ground one day The equator is the dividing line between the southern hemisphere and the northern hemisphere. It divides the earth into two hemispheres, the northern hemisphere is in the north and the southern hemisphere is in the south, which is the baseline for dividing latitude. The equatorial latitude is 0 degrees, which is the longest latitude on the earth. At the same time, the equator is the place with the smallest acceleration of gravity on the earth.
The law of linear velocity of the earth's rotation is that the equatorial linear velocity is the fastest, decreasing to the north and south poles, and the north and south poles are wireless. Radius of the earth is about 637 1km, so the length of the equator is about 4000km, that is, 80,000 miles, which is the point on the equator. In one day, the earth has traveled 80,000 miles due to its rotation, so there is a poem "sitting on the ground and traveling 80,000 miles a day, looking at thousands of rivers".
The linear speed of rotation at the equator is about1667 km/h. Then, with the increase of latitude, the linear speed of rotation decreases continuously. At the north and south poles, the latitude circle is as small as one point and there is no linear speed. Because of the rotation of the earth, a series of geographical meanings have been produced.