2. Newton systematically summarized the work of Galileo, Kepler and Huygens, and got the famous law of universal gravitation and Newton's three laws of motion.
In the book Mathematical Principles of Natural Philosophy, Newton started with the basic concepts of mechanics (mass, momentum, inertia and force) and the basic laws (three laws of motion), and used the sharp mathematical tool of calculus invented by him.
It not only demonstrated the law of universal gravitation mathematically, but also established classical mechanics as a complete and rigorous system, unified celestial mechanics and ground object mechanics, and realized the first large-scale synthesis in the history of physics.
Extended data
1, Newton's first law
(1) Motion is an attribute of an object, and the motion of the object needs no force to maintain.
(2) The law states that any object has inertia.
(3) An object that is not stressed does not exist.
Newton's first law cannot be directly verified by experiments, but it was discovered by logical reasoning of thinking on the basis of a large number of experimental phenomena.
It tells people another new way to study physical problems: by observing a large number of experimental phenomena and using human logical thinking, we can find the laws of things from a large number of phenomena.
2. Newton's second law
(1) Newton's second law quantitatively reveals the relationship between force and motion, that is, knowing the force, we can analyze the motion law of an object according to Newton's second law; Conversely, if we know the motion, we can study its force according to Newton's second law, which provides a theoretical basis for designing and controlling the motion.
(2) The mathematical expression F of Newton's second law cannot regard ma as a force.
(3) Newton's second law reveals the instantaneous effect of force. That is to say, the force acting on an object has an instantaneous corresponding relationship with its effect. When the force changes, the acceleration will also change. If the force is removed, the acceleration will be zero. The instantaneous effect of attention is acceleration rather than speed.
3. Newton's third law
Application: overweight and weightlessness
(1) Overweight: An object is said to be overweight if it has upward acceleration. The pressure F N of the overweight object on the supporting surface (or the pulling force on the hook) is greater than the gravity mg of the object, that is, F N =mg+ma.
(2) Weightlessness: An object is said to be weightless if it has downward acceleration. The pressure FN of the weightless object on the supporting surface (or the pulling force on the hook) is less than the gravity mg of the object, that is, FN=mg-ma. When a=g and F N =0, the object is completely weightless.
(3) Problems that should be paid attention to in understanding overweight and weightlessness.
No matter whether the object is weightless or overweight, the gravity of the object itself does not change, but the resultant force of the object and the support =ma, where F is the force and ma is the effect of the force, and the direction of special attention remains unchanged.
Overweight or weightlessness has nothing to do with the speed of the object, but only depends on the direction of acceleration. "Accelerated descent" and "decelerated ascent" are weightless states.
In the state of complete weightlessness, all physical phenomena usually caused by gravity will disappear completely, such as the simple pendulum stops, the balance fails, the object immersed in water is no longer buoyed, and the liquid column no longer produces pressure.
Baidu encyclopedia-Newton