Newton's Laws of Motion

Sir Isaac Newton is not only famous for his work on the laws of motion, but also contributed greatly to a wide variety of subjects, the major ones being Gravitation, Prism Optics, Diffraction, Binomial Theorem, etc. He was knighted for his exemplary studies by Queen Anne in 1705.

Newton's laws are a set of physical doctrines that describe the motion of objects as well as the field of classical mechanics. They were first described in his work titled 'Philosophiæ Naturalis Principia Mathematica', and have completely changed mankind's understanding of the universe.

These laws can be applicable only when they are studied with respect to the Newtonian frames of reference or from an inertial viewpoint. Simply said, they were studied with respect to a homogeneous and non-entropic environment.

These laws of motion were taken over by several recent theories like Einstein's Theory of Special Relativity, but as they began an important era of greater scientific understanding, they are still referred to, from a knowledge-based perspective. The following paragraphs describe each law briefly with appropriate examples.

Explanation: This is universally used as a definition of inertia. If there is no net force resulting from unbalanced forces acting on an object, the object will maintain a constant velocity. This object will remain at rest if this velocity is zero. If an additional external force is applied, the velocity will change.

Examples: For instance, on a frictionless surface, a ball would continue to remain at rest until pushed. Once in motion, it will continue moving in a straight line until a force causes it to stop or change direction.

Take a tumbler and place a cardboard piece on it. Now, put a coin on this piece, and pull out the cardboard with a jerk. What happens? If you do it properly, the coin will drop into the tumbler. The reason behind this is the 'inertia of rest'. The force was applied on the cardboard, and the coin is left behind because of its inertia.

Explanation: The acceleration of an object is directly proportional to the force applied to that object, in the direction of the force. This law is expressed by the equation, F = ma, where 'F' stands for the net force that is acting on an object.

If this body of mass 'm' has an acceleration 'a' (change in velocity with time), then the net force 'F' acting upon that object is the product of its mass and acceleration. This body also undergoes acceleration during its movement.

In simpler words, the acceleration produced by a particular force acting on a body is directly proportional to the magnitude of the force, and inversely proportional to the mass of the body.

Example: You are pushing a table across a frictionless surface. If you want to increase the speed of the table's movement (increase in acceleration), you push harder. If the table was replaced with a heavier one, you have to push even more harder than the previous time (increase in force) to speed it up at the same rate as before.

Explanation: If a force is applied by an object 'X' upon another object 'Y', then the latter will also exert an equal and opposite force on the former one. When a shooter fires his gun, he experiences a sudden recoil of the gun.

This 'kick' felt by the shooter is the reaction force, which acts upon the firearm. This force is equal in magnitude to the force that pushes forward the bullets.

Example: How do airplanes fly at high altitudes, and how are spacecrafts propelled into space? The airplanes use jet engines, i.e., engines that burn fuel at high temperatures, and expel it in the backward direction.

In this case, a force is exerted on the object's body, which, in turn, exerts an equal and opposite forward force on the ground surface. The same principle applies to spacecrafts.

Newton's laws have been validated by their application in numerous theories that were developed later, especially in the last century. The phenomenon of gravitation explained by Galileo perfectly explains the force of gravity, and the correlation or association of this force with the laws of motion.

Several other proven concepts like General Relativity, Quantum Mechanics, Classical Thermodynamics, etc., included these laws as a major part of their derivations.

These doctrines have a significant use in several engineering applications. Without these fundamentals, many modern technologies would not have been possible.