One object moves around another object along the circumference of a certain track; The trajectory can be circular, elliptical, hyperbolic or parabolic.

2, the earth rotation:

Seen from the North Pole, the rotation of the earth around its axis from west to east is counterclockwise, and from the South Pole it is clockwise. The earth's rotation axis forms an angle of 66.34 degrees with the ecliptic plane and is perpendicular to the equatorial plane.

3, clock rotation:

Mechanical clocks and watches take clockwork as the power system, and drive the escape governor through a transmission system composed of a group of gears; Then the speed of the transmission system is controlled by the escape governor in turn; The transmission system drives the pointer mechanism while pushing the escapement mechanism, and the rotation speed of the transmission system is controlled by the escapement mechanism, so the pointer can indicate the time on the dial according to certain rules; The winding pointer system is a mechanism for winding springs or moving pointers.

4, the four seasons change:

The four seasons that alternate in a year, namely, spring, summer, autumn and winter, last for three months. All the year round is formed because the earth revolves around the sun. Because of the declination angle, the direct point of the sun moves back and forth between the north and south latitudes of the earth 23 26', which causes the seasonal variation of the height of the sun at noon and the length of day and night.

5, traffic lights:

It is generally composed of red light, green light and yellow light. Red light means no traffic, green light means permission, and yellow light means warning. At first, there were only two colors, red and green. Later, after improvement, yellow light was added, red light means stop, yellow light means preparation, and green light means passage.