What are the three laws of classical mechanics?

When all objects are not subjected to external force or the resultant force is zero, their motion remains unchanged, including the state of uniform linear motion with acceleration always equal to zero and the state of rest, until an external force forces them to change this state.

2, Newton's second law:

The acceleration of an object is directly proportional to the external force and inversely proportional to the mass of the object, and the direction of acceleration is the same as that of the external force.

Formula: F (together) =kma When F (together), M and A adopt the international system of units N, kg and m/s? ，k= 1

3, Newton's third law:

The acting force between two objects is equal in magnitude and opposite in direction, and they are on the same straight line.

Scope of application of three laws of classical mechanics;

It is very accurate on many occasions. Classical mechanics can be used to describe the motion of human-sized objects (such as gyroscopes and baseball), many celestial bodies (such as planets and galaxies) and some micro-scale objects (such as organic molecules). Classical mechanics is very practical in low-speed moving objects. Although Einstein put forward the theory of relativity, we seldom encounter high-speed motion (light speed) in our life, so we will still explain various phenomena with classical mechanics. But between high-speed motion or objects with great mass, classical mechanics is "? The heart is more than enough, but the strength is insufficient. " This is also the category of modern physics.

Extended data:

The basic laws of classical mechanics are Newton's laws of motion or other mechanical principles related to Newton's laws and their equivalents. This is mechanics before the 20th century, and there are two basic assumptions:

1, assuming that time and space are absolute, the measurement of length and time interval has nothing to do with the observer's movement, and the transfer of interaction between substances is instantaneous;

2. All observable physical quantities can be measured infinitely accurately in principle.

Since the 20th century, due to the development of physics, the limitations of classical mechanics have been constantly exposed. As the first hypothesis, it actually only applies to the case of low-speed motion compared with the speed of light. In the case of high-speed movement, time and length are no longer considered to be irrelevant to the observer's movement. The second assumption only applies to macroscopic objects. In microscopic systems, in principle, all physical quantities cannot be accurately determined at the same time. Therefore, when macroscopic objects move at low speed, the classical laws of mechanics are generally only approximate laws.

References:

Baidu encyclopedia-classical mechanics

References:

Baidu encyclopedia-Newton's classical mechanics