Newton's three laws are important laws in mechanics and the basis of studying classical mechanics.
1, Newton's first law
Content: Any object remains in a state of static or uniform linear motion until it is forced to change this state by the force of other objects.
Description: Objects tend to stay still and move in a straight line at a constant speed, so the motion state of an object is determined by its motion speed. Without external force, its motion state will not change. This property of an object is called inertia. So Newton's first law is also called the law of inertia. The first law also clarifies the concept of force. It is clear that force is the interaction between objects, and it is pointed out that force changes the motion state of objects. Because acceleration describes the change of object's motion state, force is related to acceleration, not to speed. If we don't pay attention to this point in our daily life, we are often prone to illusion.
Note: Newton's first law does not hold true in all reference frames, but actually only in inertial reference frames. Therefore, Newton's first law is often regarded as a criterion whether a reference system is an inertial reference system.
2. Newton's second law
Content: When an object is subjected to resultant force, it will produce acceleration. The direction of acceleration is the same as the direction of resultant force, and the magnitude of acceleration is directly proportional to resultant force and inversely proportional to the inertial mass of the object.
The second law quantitatively describes the function of force and quantitatively measures the inertia of an object. It is a relationship between vector and instantaneous.
It should be emphasized that the resultant force acting on the object will produce acceleration, which may change the motion state or speed of the object, but this change is related to the motion state of the object itself.
In a vacuum, because there is no air resistance, all kinds of objects are only affected by gravity, so the acceleration is the same regardless of the mass. Therefore, in free fall, in the same time interval, their speed changes are the same.
3. Newton's third law
Content: The acting force and reaction force between two objects are on the same straight line, equal in magnitude and opposite in direction.
Note: To change the motion state of an object, other objects must interact with it. The interaction between objects is embodied by force. It is pointed out that the role of output is mutual, and there is a reaction when there is a role. They act on the same straight line, equal in size and opposite in direction.
Newton's law of motion is an important law in mechanics and the basis for studying classical mechanics and even physics. The basic laws of motion in classical mechanics are expounded. The application scope of this law is the inertial reference system given by Newton's first law of motion, which makes it meaningful for people to study physical problems and measure physical quantities. ?
Newton's law of motion refuted Aristotle and others' wrong views on the concept of force, which lasted for more than two thousand years and laid the foundation for establishing a correct concept of force. This law scientifically defines several basic concepts in classical mechanics such as inertial mass and force, and lays a conceptual foundation for the principle of particle mechanics system established by Newton's law of motion.