Newton’s II Law of Motion

Newton’s second law of motion gives a relationship between force and acceleration. In fact, it gives a measurement of force on a body.







When a car starts from rest, its velocity goes on increasing. The engine of the car applies force on it to change the velocity. Similarly, if brakes are applied on the moving car, the velocity of the car goes on decreasing. In this case, the brakes of the car apply force to decrease the velocity. In both cases, there is a change in velocity. The change in velocity is a measure of acceleration. Hence, if a force is applied, there is a change in velocity and hence there is acceleration. Conversely, if there is a change in velocity, there must be force acting on the body. This implies that there exists a relationship between the force applied and the acceleration produced on a body. Newton established the relationship between the force acting on a body and the acceleration produced on it. The relation is known as Newton’s II law of motion.

Newton’s I Law of Motion

Statement: Newton’s First law of motion states that every body in this universe continues in its state of rest or uniform motion in a straight line unless it is acted upon by an external force.



a. This means that if a body is at rest, it remains at rest until an external force compels it to change the rest state. Similarly, if a body is in motion, it continues to be in motion unless an external force compels it to change its motion state. This in facts is called law of inertia. Hence, Newton’s first law of motion is also known as law of inertia.
Examples: In our daily life, there are a large number of examples where Newton’s first law of motion can be applied. Out of these, the following are some of the most common examples:


When a papaya tree is shaken, the papaya falls

When a moving bus suddenly stops, the passengers sitting in it fall forward.


 When a horse at rest suddenly starts moving, the horse rider falls backward.

SI system

The CGS, MKS and FPS systems used only three fundamental quantities (mass, length and time) for the measurement of a physical quantity. However, these three fundamental quantities were found insufficient to measure some physical quantities in thermodynamics, optics and current electricity. For example, the amount of current in a circuit could not be expressed in terms of mass, length and time. To solve the problem, another system of unit called SI(System International de Units) units came into existence. In fact, the international convention of scientists held in France in 1968 decided to use the SI units. In addition to mass, length and time as the fundamental quantities, the SI units added a few more quantities as the fundamental quantities. They are temperature, electric current, luminous intensity and amount of substances.