The content of Newton's first law: all objects always keep moving in a straight line or at rest until an external force forces them to change this state.

Newton's second law: the acceleration a of an object is directly proportional to the resultant force f and inversely proportional to the mass m of the object, and the direction of acceleration is the same as that of the resultant force.

Newton's third law: the action and reaction between two objects are always equal in size and opposite in direction, and act on a straight line.

What is the scope of application of Newton's three laws?

1. Classical mechanics is suitable for low-speed motion and macroscopic objects, but not for high-speed and microscopic objects.

2. Newton's laws of motion include Newton's first law, Newton's second law of motion and Newton's third law of motion, which were summarized and put forward by isaac newton in his book Mathematical Principles of Natural Philosophy 1687.

3. Among them, the first law explains the meaning of force: force is the reason to change the motion state of an object; The second law points out the role of force: force makes an object get acceleration; The third law reveals the essence of output: force is the interaction between objects.