Newton's law is a basic law in classical mechanics, which describes the relationship between motion and force. It was put forward by British physicist isaac newton in the 7th century.

1, Law of Inertia: Also known as the first law, it shows that if no external force acts on an object, it will remain in a state of static or uniform linear motion. This means that the object has inertia, that is, the motion state of the object will remain unchanged.

2. The law of motion: also known as the second law, describes the relationship between force, mass and acceleration. According to the law of motion, the acceleration of an object is directly proportional to the force exerted on it and inversely proportional to the mass of the object. The mathematical expression is F=ma, where f is the force acting on the object, m is the mass of the object, and a is the acceleration of the object.

3. Action-reaction law: also known as the third law, it shows that if one object exerts a force on another object, the second object will also exert a force of equal magnitude and opposite direction on the first object. In short, any pair of forces are interactive, equal in magnitude and opposite in direction.

Applicable conditions of Newton's law

1, ideal situation: in real life, due to the influence of friction, air resistance and other factors, it is difficult for us to find a perfect weightless environment to verify Newton's law. But through accurate experiments and measurements in the laboratory, we can verify the applicability of Newton's law to some extent.

2. Single object: Newton's law is mainly applicable to the study of a single object. When we study the interaction between multiple objects, we need to consider the relative motion and interaction between these objects.

3. Low-speed motion: Newton's law is mainly applicable to low-speed motion. When the speed of an object approaches the speed of light, Newton's law will no longer apply, because the physical phenomenon at this time has gone beyond the scope of classical mechanics.

4. Inelastic collision: Newton's law is mainly applicable to inelastic collision. In elastic collision, the object will return to its original shape and speed after collision, while in inelastic collision, the object will be deformed or broken after collision and cannot return to its original shape and speed.