The basis of classical mechanics is laid out in three assertions known as Newtons laws of motion, which were first articulated by English physicist and mathematician Isaac Newton. These laws describe the relationships between forces acting on a body and its motion.
1. First law of Newton: The law of inertia
According to Newtons first law, if a body is at rest or moving in a straight line at a constant speed, it will continue to move at that speed or remain at rest until acted with by a force. In fact, according to classical Newtonian mechanics, there is no significant difference between being at rest and moving uniformly in a straight line; they can both be thought of as states of motion experienced by different observers, one of whom moves at the same speed as the particle and the other of whom moves at a constant speed in relation to the particle. The law of inertia is the name given to this postulate.
2. Newtons second law of motion : F = ma
Newtons second law provides a precise explanation of the modifications that a force can make to a body motion. According to this, a body momentum changes at a rate that is equal to the force acting on it over time in both magnitude and direction. A body momentum is equal to the sum of its mass and velocity. Similar to velocity, momentum has both a magnitude and a direction, making it a vector quantity. When a force is applied to a body, the momentum magnitude, direction, or both can change. One of the most significant laws in all of physics is Newtons second law. It is possible to express this in the form F = ma for a body whose mass m is constant. Here, F is force and a is acceleration and both are vector quantities.
If no force acts on the system, then no acceleration is produced.
3. Newtons third principle : The law of action and reaction
According to Newtons third law, when two bodies come into contact, they exert forces on one another that are equal in size and directed in the opposite direction. The law of action and reaction is another name for the third law. This law applies to bodies in uniform or rapid motion and is crucial for addressing problems of static equilibrium, where all forces are in balance. The forces it discusses are actual phenomena, not just accounting tricks. A book laying on a table, for instance, exerts downward pressure equal to the weight of the book on the table. The third law states that the book is subject to an equal and opposing force from the table.