Definition: In mechanics, length, mass, and time are regarded as basic quantities, and the units are meters (m), kilograms (kg), and seconds (s).
Export units
Definition: The units of other physical quantities derived from the units of basic physical quantities based on the relationships between physical quantities.
Newton's first law
Definition: All objects always maintain a state of uniform linear motion or a state of rest unless a force forces it to change this state.
Force is not what keeps an object moving, but what changes its state of motion.
The object itself has the property of maintaining a state of uniform linear motion or a state of rest. This state is called inertia.
Newton's second law
The acceleration of an object is related to both the force on the object and the mass of the object
Definition: The acceleration of an object is directly proportional to the force on the object and inversely proportional to the mass of the object. The direction of acceleration is the same as the direction of the force.
The mass of an object is a measure of its inertia
When the mass of an object is constant, the acceleration is proportional to the net force
When the resultant force is constant, the acceleration of an object is inversely proportional to its mass.
Newton's third law
A pair of forces that interact between objects, we call any one of them an action force and the other a reaction force
Definition: A pair of action force F and reaction force F’ between two objects are always equal in magnitude and opposite in direction, acting on the same straight line.