What Is the Law of Universal Gravitation?

^{[1] The} law of gravity was published by Isaac Newton in The Mathematical Principles of Natural Philosophy in 1687. Newton's universal law of gravity is expressed as follows:

Introduction

Although Newton's description of gravity is very accurate for many practical applications, it also has several major theoretical problems and proved to be incomplete.

The mutual attraction caused by mass between any two objects. The line of force is about the line connecting the centers of mass of the two objects. Its magnitude is proportional to the mass of the two objects and inversely proportional to the square of the distance between the two objects. . The law of universal gravitation was discovered by Newton's pursuit of gravity on objects on the ground, and was officially published in 1687. Let m ₁ and m ₂ represent the masses of the two objects, and r represents the distance between the two, then the mutually attractive forces F are:

, Where G is called the universal gravitational constant. This is the mathematical expression of the law of gravity. Strictly speaking, the above formula is for two particles. Because the term "distance between two objects" refers to the distance between two particles. If one is a mass point and the other is a finite body, the finite body can be divided into many mass points and the vector sum of their gravitational forces can be obtained to obtain the force of the entire finite body on the mass point. Newton has proved that the gravity of a sphere with a density as a function of the distance r from the center of the sphere to a particle outside the sphere is no different from the situation where the entire sphere mass is concentrated at the center of the sphere. Newton used the law of universal gravity to prove natural phenomena such as Kepler's law, the motion of the moon around the earth, the cause of the tides and the flattening of the poles of the earth. Newton's law of gravity is the basis of celestial mechanics. The orbits of satellites, moons and planetary probes are calculated based on this law. The experimental proof of the existence of universal gravitation and the determination of the gravitational constant G were made by Cavendish in 1798. The current accepted value of the gravitational constant is G = 6.6732 × 10¹¹ m² / kg · s².

In 1859, French astronomer Levier discovered that the value of the precession rate of Mercury's perihelion was deviated from the value calculated by the law of gravitation by 38 per 100 years (the measurement value of American astronomer S. Newcom was 43 ). In 1915, Einstein founded the general theory of relativity, finally explained this problem, and predicted the deflection of light in the gravitational field and the red shift of the spectrum. Astronomers have also predicted the existence of black holes, bringing general relativity into a new realm related to the evolution of the universe. Einstein denied the existence of the inertial coordinate system in cosmic space with the equivalence of the acceleration coordinate system and the gravitational field, and changed the space characteristics with the gravitational field. He believes that the motion of an object in the gravitational field is a short-range line along a four-dimensional curved Riemann space. But in the case of weak gravitational fields (such as the solar system), for many mechanical problems, it is much simpler to use Newton's law of universal gravitation than to use Einstein's general theory of relativity. For the simple two-body problem, it is difficult to use mathematical theory of general relativity because of the mixed concept of "simultaneity".

In the microscopic world where particles interact, universal gravitation is the weakestspecies. The unity of universal gravitation, electromagnetic force, and nuclear force needs further efforts from scientists.

1, entry Author: Jia He. "Encyclopedia of China" Volume 74 (First Edition) Mechanics Entry: Gravity: China Encyclopedia Press, 1987: 490 pages.