Imagine throwing a rock into a pond of still water. There is an initial splash, followed by a ripple that eventually peters out. The larger the rock you throw, the larger the wave and the longer it takes for the pond to become still again. Though it produces a different kind of wave, sound travels through air in a similar way. A vibrating object causes pressure on the air molecules around it. These air molecules push on other air molecules and so on, creating a wave that expands away from the source of the vibration. This is known as a "longitudinal" wave, which means that it propagates parallel to the displacement of its medium.
Speed
The speed of sound through air is not always the same. It depends on air temperature. This is because air molecules collide with each other more rapidly at higher temperatures. According to Hypertextbook.com, the speed of sound through air at 20C (room temperature) is approximately 343 meters per second. Compare this to 386 meters per second in air at 100C.
Wavelength
The wavelength of a sound wave is the distance from the peak (high point) of one wave to the peak of the next. The shorter this distance, the closer the waves are together and the higher the pitch of the sound. Longer wavelengths are indicative of sound with lower pitch.
Frequency
Frequency is the number of cycles a wave completes in a given amount of time. The standard unit for measuring sound frequency is hertz (Hz); 1 Hz is equal to 1 cycle per second. The shorter a sound's wavelength, the closer its peaks will be to each other. Thus, it will be at a higher frequency than a sound with a longer wavelength, because it will cycle more often in a given amount of time. Think of piano strings: When the shortest string is struck, there is much less material available to absorb the impact as compared to the longest string. The short string vibrates faster, creating a wave with a shorter wavelength and a higher pitch.
Amplitude
According to MediaCollege.com, amplitude represents the strength of the wave, a property we interpret as volume. The higher the amplitude, the longer it takes for the wave to dissipate in the air and the sound to fade. Note that an amplifier increases the amplitude of a given sound; its purpose is to increase the volume of a sound without affecting its pitch.
Hearing
Not all objects causing vibrations through the air create waves that are detectable by the human ear. Generally speaking, the human ear is capable of hearing frequencies between 20 Hz and 20 kHz (20,000 Hz). A sound at 20 Hz is the lowest, "bassiest" pitch a person can hear, while a sound at 20 kHz is the highest. A dog whistle operates at frequencies up to 22 kHz. It operates on the same principle as a normal whistle, only outside the frequency range of the human ear.
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