SPEED OF SOUND The speed of sound in air is approximately 331.5 m/sec at 0C. Sound speed lowers at lower temperatures and increases at higher temperatures. Sound speed increases at a rate of approximately 0.6 m/sec for every 1C increase in temperature.

The speed of sound in water is about 4 times greater than the speed of sound in air. Seawater is more dense than fresh water; therefore, at the same temperature, the speed of sound in sea will be slightly greater than the speed of sound in fresh water.

In steel, sound speed is about 15 times greater than in air. Sound travels at approximately 5,200 m/sec through a thin steel rod.

A detector acts as a receiver of sound. The detector permits us to tell whether sound has been produced. Sound travels in waves that move radially (360 degrees) from their source, and only a small part of a waves energy reaches a detector. Therefore, detectors often contain amplifiers to boost a signals energy, thereby permitting reception of weak signals.

Learning Objective: Identify the various properties of sound waves.

SOUND WAVES 

Sound travels in the form of waves. Sound waves are brought about by vibrations within a medium. The vibrations produce compressions (pressure increases) and rarefactions (pressure decreases) that impact the particles within the medium. The particles do not physically move, but the energy is transferred from particle to particle. This is how the sound travels. A single sound wave consists of one compression and one rarefaction.

The length of a sound wave is the distance between any two successive compressions or rare fractions. Figure 2-1-2 illustrates a longitudinal wave with its compressions and rarefractions. One complete wavelength is called a cycle. Wavelengths vary depending on the number of cycles per second produced by the sound source.

The number of cycles per second (cps) is a measure of a sounds frequency. The higher the frequency, the shorter the wavelengths, and vice versa. 

Frequencies are measured in the Hertz system, 1 hertz (Hz) is equal to 1 cycle per second (cps). Frequencies of 1000 Hz or more are measured in kilohertz (kHz). The average human hears sounds between 20 Hz and 15 kHz, while sounds below

Figure 2-1-2.-Longitudinal wave.

20 Hz and above 15 kHz are normally beyond the human range of hearing.

The pitch of a sound depends on the frequency of the sound as received at a detector. The human ear detects sounds and classifies them based on the sound quality. Some sounds are harsh, while others are pleasant. Pitch is a subjective quality dependent on the receiver.

Privacy Statement - Press Release - Copyright Information. - Contact Us - Support Integrated Publishing