The speed of sound is around 1,230 kilometres per hour (or 767 miles per hour).This gives each musical instrument its characteristic sound. But if we were to sing or play a note on a trumpet or violin, the result is a combination of one main frequency with other tones. If we strike a tuning fork, it gives off a pure tone, which is the sound of a single frequency. The sounds we hear every day are actually collections of simpler sounds. When the vocal cords are stretched we make high sounds and when they are loose we make lower sounds. We change the sounds we make by stretching those vocal cords. To speak, we move air past our vocal cords, which makes them vibrate. Speaking (as well as hearing) involves vibrations. ( Transverse waves occur when the molecules vibrate up and down, perpendicular to the direction that the wave travels). Sound energy causes the molecules to move back and forth in the same direction that the sound is travelling. When molecules in a medium vibrate, they can move back and forth or up and down. This means that sound travels faster through water than through air, and faster through bone than through water. When a wave passes through a denser medium, it goes faster than it does through a less-dense medium. The properties of a sound wave change when it travels through different media: gas (e.g. These bones make larger vibrations within the inner ear, essentially amplifying the incoming vibrations before they are picked up by the auditory nerve. Attached to the eardrum are three tiny bones that also vibrate: the hammer, the anvil, and the stirrup. These vibrations enter the outer ear and cause our eardrums to vibrate (or oscillate). When we hear something, we are sensing the vibrations in the air. For example, adding water causes the glass to get heavier (increase in mass) and thus harder to move, so it tends to vibrate more slowly and at a lower pitch. This sound can be changed, however, by altering the vibrating mass of the glass. For example, if you ‘ping’ a glass with your finger, the glass will produce a sound at a pitch that is its natural frequency. This is known as the natural frequency of the object. When these objects vibrate, they tend to vibrate at a particular frequency or set of frequencies. Nearly all objects, when hit, struck, plucked, strummed or somehow disturbed, will vibrate. For example, a heavy E string on an instrument can be made to sound higher than a thin E string by tightening the tuning pegs, so that there is more tension on the string. However, the pitch can be altered by changing the tension or rigidity of the object. Generally, the greater the mass, the more slowly it vibrates and the lower the pitch. The pitch of a sound is largely determined by the mass (weight) of the vibrating object. Sound waves themselves do not have pitch their vibrations can be measured to obtain a frequency, but it takes a human brain to map them to that internal quality of pitch. That is, while frequency is objective, pitch is completely subjective. Frequency is the scientific measure of pitch. Pitch is related to frequency, but they are not exactly the same. The number of vibrations per second is referred to as an object’s frequency, measured in Hertz (Hz). Cats can hear even higher pitches than dogs, and porpoises can hear the fastest vibrations of all (up to 150,000 times per second!). The fastest vibration we can hear is 20,000 vibrations per second, which would be a very high-pitched sound. The slowest vibration human ears can hear is 20 vibrations per second. For example, we would not be able to hear the slow vibrations that are made by waving our hands in the air. However, the vibrations need to be at a certain speed in order for us to hear them. If your ear is within range of such vibrations, you hear the sound. As it is disturbed, each molecule just moves away from a resting point but then eventually returns to it. As a result, there is a series of molecular collisions as the sound wave passes through the air, but the air molecules themselves don’t travel with the wave. This “chain reaction” movement, called sound waves, keeps going until the molecules run out of energy. These molecules bump into the molecules close to them, causing them to vibrate as well. This makes them bump into more nearby air molecules. When an object vibrates, it causes movement in surrounding air molecules. Sound is a type of energy made by vibrations. Understand how our inner ear contributes to hearing.ĭescribe what pitch is and how it varies.
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