This law states that if an object is at rest or moving in a straight line at a constant speed, it will remain at rest or continue to move in a straight line at a constant speed as long as there is no external force acting on it. This law is also called the law of inertia, which describes a property of force: force can make an object move from rest to motion and from motion to rest, and it can also cause an object to change from one form of motion to another. This is called Newton's first law. The most important question in mechanics is how objects move under similar circumstances. Newton's second law solves this problem; it is considered the most important fundamental law of classical physics. Newton's second law quantitatively describes how force can change the motion of an object. It explains the time rate of change of velocity (that is, acceleration a is directly proportional to force F and inversely proportional to the mass of the object, that is, a=F/m or F=ma; the greater the force, the greater the acceleration; the greater the mass, The smaller the acceleration. Both force and acceleration have both magnitude and direction. Acceleration is caused by force, and the direction is the same as force. If there are several forces acting on an object, the acceleration is caused by the resultant force. The second law is the most important. , from which all the fundamental equations of power can be derived by calculus. Furthermore, Newton formulated his third law based on these two laws. Newton's third law states that the interaction of two bodies is always equal in magnitude and opposite in direction. For two objects in direct contact, this law is relatively easy to understand. The downward pressure of the book on the table is equal to the upward force of the table on the book, that is, the action force is equal to the reaction force. The same is true for the gravitational force. A flying airplane pulls the earth upward. The force is numerically equal to the force of the earth pulling down on the plane. Newton's laws of motion are widely used in science and dynamics. Newton's laws of motion are a general term for the three laws of motion in physics proposed by Isaac Newton. Known as the foundation of classical physics, it is Newton's first law (law of inertia): All objects, without the influence of any external force, always maintain a state of uniform linear motion or rest until an external force forces it to change this state. . - It clarifies the relationship between force and motion and proposes the concept of inertia)", "Newton's second law (the acceleration of an object is directly proportional to the net external force F on the object, and inversely proportional to the mass of the object. The direction of the acceleration Same as the direction of the net external force) Formula: F=kma (when the unit of m is kg and the unit of a is m/s2, k=1), Newton's third law (the action and reaction force between two objects, On the same straight line, they are equal in magnitude and opposite in direction)" Optical contribution Before Newton, Mozi, Bacon, Leonardo da Vinci and others had studied optical phenomena. The law of reflection is one of the optical laws that people have known for a long time. . When modern science began, Galileo discovered the "new universe" through telescopes, which shocked the world. The Dutch mathematician Snell first discovered the law of refraction of light... Newton and others were similar to him. At the same time, Hooke, Huygens and others, like their predecessors such as Galileo and Descartes, studied optics with great interest and enthusiasm. In 1666, while on vacation at home, Newton obtained a prism, which he used to conduct research. He performed the famous dispersion experiment. After a beam of sunlight passes through a prism, it is decomposed into several color spectral bands. Newton then uses a baffle with a slit to block the other colors of light, allowing only one color of light to pass through. The results of the two prisms were only the same color of light. In this way, he discovered that white light is composed of various colors of light. This was his first major contribution. In order to verify this discovery, Newton tried to combine several different colors. Monochromatic light was synthesized into white light, and the refractive index of different colors of light was calculated, which accurately explained the dispersion phenomenon. The mystery of the color of matter was revealed. It turns out that the color of matter is the different reflectivity and refraction of light of different colors on objects. caused by the rate. In 1672 AD, Newton published his research results in the "Philosophical Journal of the Royal Society". This was his first publicly published paper. Many people studied optics to improve refracting telescopes. Because Newton discovered the composition of white light, he believed that the dispersion phenomenon of refracting telescope lenses could not be eliminated (later, some people used lenses composed of glasses with different refractive indexes to eliminate the dispersion phenomenon), so he designed and built a reflecting telescope.Newton was not only good at mathematical calculations, but he was also able to make various experimental equipment and conduct precise experiments by himself. In order to manufacture telescopes, he designed his own grinding and polishing machine and experimented with various grinding materials. In 1668 AD, he made the first prototype of a reflecting telescope, which was his second greatest contribution. In 1671 AD, Newton presented his improved reflecting telescope to the Royal Society. Newton became famous and was elected as a member of the Royal Society. The invention of the reflecting telescope laid the foundation for modern large-scale optical astronomical telescopes. At the same time, Newton also conducted a large number of observation experiments and mathematical calculations, such as studying the abnormal refraction phenomenon of glacial rocks discovered by Huygens, the color phenomenon of soap bubbles discovered by Hooke, the optical phenomenon of "Newton's rings", etc. Newton also proposed the "particle theory" of light, believing that light is formed from particles and takes the fastest linear motion path. His "particle theory" and later Huygens' "wave theory" constitute the two basic theories about light. In addition, he also produced various optical instruments such as Newton's color disk. Constructing a building of mechanics Newton is the master of classical mechanics theory. He systematically summarized the work of Galileo, Kepler, Huygens and others, and obtained the famous law of universal gravitation and Newton's three laws of motion. Before Newton, astronomy was the most prominent subject. But why do planets must orbit the sun according to certain rules? Astronomers cannot explain this problem satisfactorily. The discovery of universal gravitation shows that the motion of stars in the sky and the motion of objects on the ground are governed by the same laws - the laws of mechanics. Long before Newton discovered the law of universal gravitation, many scientists had seriously considered this issue. For example, Kepler realized that there must be a force at work to keep the planets moving along the elliptical orbit. He believed that this force was similar to magnetism, just like a magnet attracting iron. In 1659, Huygens discovered from studying the motion of a pendulum that a centripetal force is needed to keep an object moving in a circular orbit. Hooke and others thought it was gravity, and tried to deduce the relationship between gravity and distance. In 1664, Hooke discovered that the orbital bending of comets when approaching the sun was due to the gravitational effect of the sun; in 1673, Huygens deduced the law of centripetal force; in 1679, Hooke and Halley derived the law of centripetal force from the law of centripetal force and Kepler's third law. It turns out that the gravitational force that maintains planetary motion is inversely proportional to the square of the distance. Newton himself recalled that around 1666, he had already considered the issue of gravity when he lived in his hometown. The most famous saying is that during holidays, Newton often sat in the garden for a while. Once, as happened many times in the past, an apple fell from the tree... The accidental falling of an apple was a turning point in the history of human thought. It opened the mind of the man sitting in the garden. It caused him to ponder: What is the reason why all objects are almost always attracted towards the center of the earth? Newton thought. Finally, he discovered gravity, which was of epoch-making significance to mankind. The brilliance of Newton was that he solved mathematical argument problems that Hooke and others could not solve. In 1679, Hooke wrote to ask Newton if he could prove that the planets move in elliptical orbits based on the law of centripetal force and the law that gravity is inversely proportional to the square of the distance. Newton did not answer this question. When Halley visited Newton in 1685, Newton had already discovered the law of universal gravitation: there is a gravitational force between two objects, and the gravitational force is inversely proportional to the square of the distance and directly proportional to the product of the masses of the two objects. At that time, accurate data such as the radius of the earth and the distance between the sun and the earth were already available for calculation. Newton proved to Halley that the earth's gravity is the centripetal force that causes the moon to move around the earth. He also proved that under the influence of the sun's gravity, the motion of the planets complies with Kepler's three laws of motion. At Halley's urging, Newton wrote his epoch-making great work "Mathematical Principles of Natural Philosophy" at the end of 1686. The Royal Society lacked funds and could not publish this book. Later, with Halley's funding, this one of the greatest books in the history of science was able to be published in 1687.
In this book, Newton started from the basic concepts of mechanics (mass, momentum, inertia, force) and basic laws (three laws of motion), and used the sharp mathematical tool he invented, calculus, to not only demonstrate mathematically The law of universal gravitation established classical mechanics as a complete and rigorous system, unified the mechanics of celestial bodies and the mechanics of objects on the ground, and achieved the first major synthesis in the history of physics. Newton's three major equilibria: the law of the immortality of matter, which states that the mass of matter is immortal; the law of conservation of energy, which states that the energy of matter is conserved; and the law of conservation of momentum. Newton's formula Suppose X1 represents the distance between the object and the first focus, and X2 represents the distance between the light image and the second focus X1 The symmetry is more obvious and easier to use.