Railway Science (Physics-Miscellaneous)

SONAR (Sound navigation and Ranging) is used to determine the depth of water and to locate the underwater objects. By Sonar, ultrasonic waves are transmitted towards the bottom of water, their waves are reflected by any object or bottom, total time is recorded and multiplied with the speed of ultrasonic waves, to find the depth.

SONAR (Sound Navigation And Ranging): Works by emitting high-frequency ultrasonic waves (above 20 kHz), and then detecting the echoes that bounce back from objects in the water. Uses: Military and civilian navigation, submarine detection, fish finding, underwater mapping, and scientific research. Speed of ships is measured in Knots (One nautical mile per hour).

Example of scalar quantities - Distance (meters), speed (m/s), mass (Kg) and temperature (°C). Vector Quantities - quantities which are having magnitude as well as direction.

When an object travels faster than the speed of sound in a medium, a cone shaped region of high pressure called a shock wave trails behind it. They occur in the atmosphere during explosive events, for example during detonations or lightning strikes, or when aeroplanes break through the sound barrier. Speed of sound - about 343 meters per second.

An ultrasound is an imaging test that uses sound waves to make pictures of organs, tissues, and other structures inside your body. It allows your health care provider to see into your body without surgery and it monitors the health and development of an unborn baby during pregnancy. X-ray machines pass x-ray beams (a form of ionising radiation) through a part of the body to produce images of the tissue, organs, bones, or teeth inside. CT scan:- It shows detailed images of any part of the body, including the bones, muscles, organs and blood vessels. MRI (magnetic resonance imaging):- It is a non-invasive imaging technology that produces three dimensional detailed anatomical images.

Mass (m) represents the amount of matter in a particle or object. SI unit:- Kg. The mass (m) of an object is a fundamental property of matter that measures the amount of matter in an object. It is a scalar quantity and is always constant for a given object, regardless of where it is located. Some other scalar quantities (which have only magnitude): Length, area, volume, speed, density, pressure, temperature, energy. Vector quantities (which have both magnitude and directions): Displacement, velocity, acceleration, momentum, force.

Weight - It is the measure of the force of gravity acting on a body. Weight on the surface of earth is 1/6th on the moon's surface. Translucency - Optical and a perceptual phenomenon that characterises subsurface light transport through objects and materials. The specific heat capacity is defined as the quantity of heat (J) absorbed per unit mass (kg) of the material when its temperature increases 1 K (or 1 °C), and its units are 𝐽/(𝐾𝑔 𝐾) or 𝐽/(𝐾𝑔°𝐶) .

The rate of change of velocity is called Acceleration ( a = Δv/Δt). Velocity : The rate of change of displacement.

SI unit - meter/second² (m/s²). It is a vector quantity. It can be positive or negative both. Angular displacement, (SI unit - radian) - The shortest angle between the initial and the final position for an object in a circular motion around a fixed point. Angular momentum - The property of any rotating object given by moment of inertia times angular velocity. It is measured in kilogram meters squared per second (kg m²/s). Displacement (SI unit- meter)- Change in position of an object. It is a vector quantity.

(denoted by hf). Bore: The diameter of the hole in the center of a gear. Addendum: Radial distance of a tooth from the pitch circle to the top of the tooth (or addendum circle). Hubs: Used to transmit mechanical power from a drive motor by coupling it to an output device such as a wheel or an arm. Addendum Circle (Outside circle): Circle drawn through the top of the teeth and is concentric with the pitch circle.