Book Overview

Laws of motion explain the ways of motion by discussing why an object moves (or do not move). Isaac Newton put forth three laws of motion as mentioned below and laid the foundation of classical mechanics. A. First Law of Motion Newton′s first law of motion is also referred as “Law of Inertia”. The law states that An object at rest tends to remain at rest and an object in motion stays in motion with the same speed and in the same direction unless an external or unbalanced force is applied to it. English translation of Newton′s first law from original Latin of Newton′s Principia– Every body persists in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed. An object tends to maintain its state of motion. The state of motion of an object is defined by its velocity. According to First law of motion, an object at rest has zero velocity and will remain with a zero velocity due to the absence of unbalanced force. Such object will not change its state of motion (i.e., velocity) unless acted upon by an unbalanced force. An object in motion will (in the absence of an unbalanced force) remain in motion and will not change its state of motion (i.e., velocity) unless acted upon by an unbalanced force. A car toy kept on the surface continues to be at rest in the absence of external force. The force on the car toy due to gravitational pull and normal force is balanced and keeps the car toy at rest. The gravitational force and normal force acting upon the car toy are in equal magnitude but in opposite direction. If you apply a force onto the car toy it starts moving and continues to be in motion with same speed and in the same direction unless an external force is applied to it again. In our daily life when we apply a force on a car toy kept on the surface, it stops moving after some time. This is due to the fact that frictional force and air resistance act as unbalanced force on the car toy and changes its state of motion. Applications of Newton′s first law of motion a. When a bus suddenly starts, the passengers sitting or standing in the bus tend to fall backward. When the bus suddenly starts, the lower part of the body of the passenger which is in contact with the bus moves along with the bus while the upper part of the body tends to retain its state of rest due to inertia. As a result, the passenger falls backward. When a moving bus suddenly stops, the passengers sitting or standing in the bus are thrown forward. This is due to the reason that when the moving bus suddenly stops, the lower part of the body of the passenger attached to the bus suddenly comes to rest while the upper part of the body tends to retain its state of motion due to inertia. As a result, the passenger is thrown forward.