Railway Science (Physics-Sound)

Compression is a region in a longitudinal wave where the particles are closest together. A Rarefaction is a region in a longitudinal wave where the particles are farthest apart. When pressure becomes high, medium particles come closer and a compression is formed and due to low pressure, rarefaction is formed. Transverse waves propagate in the form of crests and troughs.

Sound waves travel through compression and rarefactions in the medium and on the other hand, light waves do not require medium to travel. Both sound and light waves follow the law of reflection i.e. the angle of incidence is equal to the angle of reflection.

Speed of sound changes in a medium at 25°C: Aluminium- 6420 m/s, Nickel- 6040 m/s, Steel- 5960 m/s, Water (Sea)- 1531 m/s, Water (distilled)- 1498 m/s, Hydrogen- 1270 m/s, Air- 346 m/s, Oxygen- 316 m/s.

Speed of Sound varies from substance to substance. Sound travels most slowly in gases, faster in liquids, and fastest in solids because the molecules are closer together and more tightly bonded in solids. Speed of sound (m/s) in different media at 25 ºC : Aluminium - 6420, Hydrogen - 1284, Brass - 4700, Glass (flint) - 3980, Iron - 5950.

Wavelength refers to the distance between two consecutive troughs or crests of a wave. Amplitude is the maximum distance or displacement reached by a point on a vibrating body. Pitch is the perception of frequency.

Bullets, jet planes etc. move at this speed. Ultrasonic sound: Its frequency is more than 20 kHz. It is produced by dolphins, bats and porpoises. Infrasonic sound (infrasound): Its frequency is below 20 Hz.

The vocal cord, situated in the larynx, is connected to the thyroid cartilage, also called the "Adam's apple". When air passes through during exhalation, the vocal cord comes together, vibrating and producing sound waves that form the voice.

Sound is a longitudinal mechanical wave. Audible range of sound for human beings 20 Hz to 20000 Hz. Children under the age of five and some animals, such as dogs can hear up to 25 kHz (1 kHz = 1000 Hz). Infrasonic sound (Infrasound) - Sounds of frequencies below 20 Hz. Produced by earthquakes, volcanic eruptions, Ocean waves, elephants, and whales. Ultrasonic waves - Frequencies greater than 20,000 Hz. Example: Bats and Dolphins. The speed of sound in the air is 346 ms⁻¹ .

It is not a characteristic of sound itself but rather a physical phenomenon that produces sound. Sound is defined as vibrations that travel through the air or another medium as an audible mechanical wave. Pitch, Quality, and Loudness are all characteristics of sound.

Sound can propagate through all three states of matter: solids, liquids, and gasses. It cannot travel through vacuum. The speed of sound depends on the properties and temperature of the medium through which it travels.