Railway Science (Physics-Miscellaneous) (Part-II)

Circular Motion: Circular motion is a movement of an object along the circumference of a circle or rotation along a circular path. Uniform circular motion: The circular motion in which the speed of the particle remains constant is called uniform circular motion. In a uniform circular motion, force supplies the centripetal acceleration.

Distance is the path traveled by the object. Displacement is the shortest distance between final and initial position. Since distance is zero hence body has not traveled any path, hence final and initial position is also same so displacement is zero.

Types of inertia : Inertia of rest - resistance of the body to change its state of rest unless acted upon by an external force. Example - When books are piled one above the other and the lowest book is suddenly pulled out, the rest of the books remain intact. Inertia of motion - tendency of a body to resist any change in its condition of uniform motion. Example - A person jumps out from a train and falls forward. Inertia of direction - When an object is moving in a direction it will remain moving in the same direction until an external force is applied. Example, when driving a car, one's body moves to the side.

Acceleration is the rate of change of velocity with time. SI unit - m/s2 . Types of Acceleration: Uniform Acceleration - An object is said to move in uniform acceleration if an equal amount of velocity increases in equal intervals of time, Example - A ball rolling down a slope, a skydiver jumping out of a plane. Non-uniform Acceleration - An object is said to be with non-uniform acceleration if the velocity of the object changes by unequal amounts in equal intervals of time, Example - A car going around a curve. Instantaneous Acceleration - The acceleration of an object at any instant of time.

Sir Isaac Newton formulated the laws of motion in the year 1686 in his book “Principia Mathematica Philosophiae Naturalis”. First Law (Inertia): Any object will remain in its existing state of motion or rest unless a net external force acts on it; Examples - The motion of a ball falling down through the atmosphere. Second Law (Force): The acceleration of an object depends on the mass of the object and the amount of force applied; F = ma. Example - An aircraft’s motion resulting from aerodynamic forces, aircraft weight, and thrust. Third Law (Action and Reaction): For every action, there is an equal and opposite reaction; Example - The motion of a jet engine produces thrust and hot exhaust gasses flow out the back of the engine, and a thrusting force is produced in the opposite direction.

Constant velocity - Speed at which an object travels equal displacements in equal times. Variable velocity - Speed at which an object has different displacements at different times. Instantaneous velocity - Constant velocity over a very short period of time. Average velocity - Total distance traveled during a time. Transverse velocity - The linear velocity of an object moving along a circular path.

(fundamental quantity). The mass of the body remains constant at every place while the weight of the body changes at every place as it depends on gravity. Fundamental quantities: Basic quantities which do not depend on any other factor and do not change with place. Examples: Length, mass, time, temperature, electric current, amount of substance. Derived quantities: A combination of two or more Fundamental quantities which changes with the place. Examples: Force, density, volume and momentum.

Inertia of motion - Tendency of a body to resist any change in its condition of uniform motion. Example - A person jumps out from a train and falls forward, the water that flows from the tap, Car with the engine off still moves due to inertia of motion.