Railway Science (Physics-Sound)

Sound is a mechanical wave and needs a material medium for its propagation. It cannot travel through a vacuum. Of the three mediums (gas, liquid, and solid), sound waves travel the slowest through gases, faster through liquids, and fastest through solids.

The sensation of sound persists in our brain for about 0.1 Second. To hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1s. An echo is a repetition or a partial repetition of a sound due to Reflection.

Echo - A repeated sound that is caused by the reflection of sound waves from a surface. Application of echo - Measuring Depth and Height, Measuring Distance, Medical Purpose. Refraction of sound waves - The bending of a sound wave owing to changes in the wave's speed. Interference of sound waves - When two or more waves interact with each other to produce a new wave.

The loudness of a sound is directly proportional to the square of the amplitude. The larger the amplitude, the louder the sound. The loudness of a sound is measured in decibels (dB). Amplitude: The maximum displacement moved by a point on a vibrating body or wave measured from its equilibrium position. It is equal to one-half the length of the vibration path. Its SI unit is metre (m).

Wave - A disturbance in a medium that carries energy without a net movement of particles. Mechanical Waves - A wave that is an oscillation of matter and is responsible for the transfer of energy through a medium. Types - Longitudinal (movement is parallel to motion of energy), Transverse waves (movement is at 90° to motion of energy). Examples - water waves, seismic waves, wind waves. Electromagnetic waves - It is created as a result of vibrations between an electric and a magnetic field. Examples - Microwaves, X-ray, Radio waves, Ultraviolet waves.

Sound waves are mechanical waves, which require a medium such as solid, liquid, or gas to vibrate and transmit the energy. They cannot propagate in a vacuum, as there are no particles to vibrate and carry the disturbance.

Dolphins communicate using ultrasonic whistle sounds, which have frequencies greater than 20,000 Hz. Infrasound refers to sound waves with frequencies below the lower limit of human hearing (20 Hz). Humans cannot detect this sound.

The sound waves of frequency greater than 20 kHz are called ultrasonic sounds. Bats, praying mantis, dolphins etc. communicate via ultrasonic sounds. The sound waves of frequency below the range of 20 Hz are called infrasonic sounds. Rhinos, hippos, elephants, whales, octopuses etc. communicate via infrasonic sounds.

The speed of sound is greatest in solids and decreases as it moves from solids to liquids and liquids to gases. A vacuum cannot conduct sound.

Sound - A form of energy, produced by vibrating objects, a mechanical wave needs a material medium like air, water, steel etc. for its propagation, cannot travel through vacuum, travel as longitudinal waves.
Frequency - The number of compressions or rarefactions taken together passing through a point in one second. Time Period - The time taken by two consecutive compressions or rarefactions to cross a point. Amplitude - the magnitude of maximum displacement of a vibrating particle. The amplitude of the wave determines the loudness. The pitch is determined by the frequency of the wave.