- Chinese name
- Precession
- Foreign name
- precession
- Alias
- Precession
- Nature
- Physical noun
- Principle 1
- Precession of gyros, wheels, etc. caused by gravity
- Principle 2
- Precession of magnetic moment of atoms subjected to electromagnetic force
- Common examples
- Precession, Mercury precession, reducer, etc
- Life application
- Flying bullets, etc
Fig. 1 Demonstration experiment of precession
Gyroscopic precession Precession of the magnetic moment of an atom subjected to electromagnetic force: The magnetic moment of an atom is in the same direction as the spin, so it receives Magnetic moment Г=M × H (M is the magnetic moment vector, H is the magnetic field intensity vector. Cross multiplication) can also produce the same effect, making the magnetic moment and spin axis precession. 
Precession movement
Perihelion precession (phenomenon is extremely exaggerated) The long axis of the star's elliptical orbit rotates slightly every time the star rotates around the sun. The rotation of the long axis is called precession. It is observed that the precession rate of Mercury is 1 ° 33 ′ 20 ″ per hundred years, while Celestial mechanics Family basis Newton Gravitational theory It is calculated that the precession rate of Mercury is 1 ° 32 ′ 37 ″ per hundred years. The difference between the two is 43 ″ per hundred years, which has been Observation accuracy There is no scope to ignore. In order to give a reasonable explanation for this difference, Le Vie, an astronomer who successfully predicted the existence of Neptune, predicted that there would be an undiscovered asteroid near the sun. Due to the effect of this asteroid, Mercury has "redundant" precession. After years of careful searching, no one found the asteroid. It seems that Levier's divine calculation failed this time. According to the classical theory of gravity, gravity is the action between matter at a distance, and the action between objects is only related to the mass and distance of objects. The gravitational field equation does not have intrinsic property (that is, the field equation does not determine the equation of motion), which means that the theory of gravity does not consider the influence of spacetime on the motion of objects. General relativity starts from the curvature of space-time and establishes the intrinsic theory of relative gravity. It is easy to explain why Mercury's perihelion precession increases by 43% every hundred years as long as the effect of space-time curvature is considered“ [1] 。
The precession reducer has the following technical features: the middle section of the input shaft is a hollow crankshaft planet gear The two tapered roller gear rings are meshed with the fixed central bevel gear on the end cover and the movable central bevel gear on the output shaft respectively. The precession reducer has multi tooth meshing performance, high bearing capacity, compact structure, small size, high transmission efficiency and reliable operation. Common examples are top 。 When the axis of its rotation axis is no longer Vertical It will be found that the rotation axis will rotate along the lead straight line, which is called "precession" phenomenon. Another example is the Earth's rotation 。 For example, take a gyroscope as an example. If you gently flick the right side of the gyroscope that rotates rapidly in a counterclockwise direction, you will find that the gyroscope will rotate forward. The gyro rotates on both sides at the same time. One is the motion of rotating along the axis, and the other is the motion of rotating around the axis. In general, the two motions of the rotary type will maintain balance. If one side of the rotating gyro is flipped to destroy the balance, the gyro will rotate forward like a reflection in order to maintain balance. Physicists call this effect "Gyroscopic Precession". This concept is easy to understand through the effect of inertia. Inertia is often stated as the tendency of moving objects to maintain motion. In this example, the motion of a rotating object is rotation. If applied to a rotating object external force The object will resist the external force by pushing back, but the reaction is delayed. top Precession also plays an important role in helicopter flight control. Since the driving ability of the helicopter's rear tail comes from the (rotating) propeller, the gyro precession plays a role. If the propeller tilts forward (in order to obtain forward speed), its counterclockwise movement requires that the propeller can provide static thrust through about 90 ° (depending on the structure of the propeller), or the propeller is on the right side of the pilot. In order to ensure the correct operation of the pilot, when the pilot pushes the "rotary bar" forward, or when the "rotary bar" is pulled backward and then pushed left, the aircraft has a corrective connection that can tilt the swashplate to the right. Precession can make the tying object loaded with huge torque loosen or tighten by itself. The crank of bicycle pedal rotates left-handed at the left hand position, so the precession can make it tighten rather than loosen. Before the screw that is not afraid of the induced torque precession appeared, the left wheel of some cars was also a left-handed screw.
For a three degree of freedom gyroscope, its precession can be used to correct or track the drift of the rotation axis; For a two degree of freedom gyroscope, its precession can be used to measure the angular velocity or angular acceleration 。 This is the principle of gyroscope. These are also widely used in aviation, aerospace, navigation and other fields. 
