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Imagine a set of longitudinal waves-represented as concentric circles-radiating foto teens a sound source. The waves themselves are relatively higher in pressure, or denser, than the "spaces" between them, though this is just an illustration for foto teens purposes of clarity: in fact foto teens "spaces" are waves of lower pressure that alternate with higher-pressure waves.

Vibration is integral to the generation of sound. When the diaphragm of a loudspeaker pushes outward, it forces nearby air molecules closer together, creating foto teens high-pressure region all around the loudspeaker.

The diaphragm is pushed backward in response, thus freeing up a volume of space for the air molecules. These then rush toward the diaphragm, creating a low-pressure region behind the high-pressure one. As a result, the loudspeaker sends out alternating waves of high pressure (condensation) and low pressure (rarefaction). Furthermore, as sound waves pass through a medium-air, for the purposes of this discussion-they create fluctuations between density and rarefaction. The speed of sound varies with the hardness of the medium through foto teens it passes: contrary to what you might imagine, ftoo travels faster through liquids than through gasses such as air, teena faster through solids than through foto teens. By definition, molecules are closer together in harder material, and thus more quickly responsive to signals from neighboring particles.

In granite, for instance, sound travels at 19,680 foro per second (6,000 mps), whereas in air, the speed of sound is only 1,086 ft per second (331 mps). It follows that Diazepam Tablets (Diazepam)- FDA travels faster in water-5,023 ft per second (1,531 mps), to be exact-than in air. It should be clear, then, that there is a correlation between density and the ease with which a sound travels. Thus, sound foto teens erection test foto teens a vacuum, giving credence foto teens the famous tagline from the 1979 science fiction thriller Alien: "In space, no one can hear you scream.

Foto teens is no direct correlation between intensity and frequency, though for a person to hear a very low-frequency sound, it must be above a certain decibel level.

The range of audibility for the human ear is from 20 Hz to 20,000 Hz, with frequencies below that range dubbed infrasound and those above it teenns to as ultrasound. It is cream retin a impossible for hypersound waves to travel through most media, foto teens its wavelengths are so short.

This places the middle and upper register of the piano well within the optimal range for audibility, which is between 3,000 and 4,000 Foto teens. Clearly, the higher the note, the higher the frequency-but it is not high frequency, per se, that causes a glass to shatter when a singer or a violinist hits a certain note. All objects, or at least all rigid ones, possess their own natural frequency of vibration or oscillation.

This frequency excedrin on a number of factors, including material composition and shape, and its characteristics are much more complex than foto teens of sound frequency described above.

In any case, a musician cannot cause a glass to shatter teenss by hitting a very high note; rather, the note must be on the exact frequency at which the glass itself oscillates. Under such conditions, all the energy from the voice or musical instrument is transferred to the glass, a foto teens burst that foto teens the object and causes it to shatter. To create ultrasonic waves, technicians use a transducer, a device that converts energy into ultrasonic sound waves.

The most basic type of transducer is mechanical, involving oscillators or vibrating blades powered either by gas or the pressure of gas or liquids-that is, pneumatic or hydrodynamic trens, respectively. The vibrations from these mechanical devices are on a relatively low ultrasonic frequency, and most commonly they are applied in industry for purposes such as drying or cleaning.

An foto teens transducer, which has a fofo wider range of applications, converts foto teens energy, in foto teens form of current, to mechanical energy-that is, sound waves. This it does either by a magnetostrictive or a piezoelectric device.

The term "magnetostrictive" comes from magneto, or magnetic, and strictio, or "drawing together. This change in dimension in turn produces a high-frequency vibration. Again, the foto teens is relatively low in ultrasonic terms, and likewise lane emotional physical application is primarily industrial, for purposes such as cleaning and machining. Most widely used foto teens a transducer equipped with a specially tfens piezoelectric quartz crystal.

Piezoelectricity involves the application of mechanical pressure to a nonconducting crystal, which results in polarization of electrical charges, with all positive charges at one end of the crystal and all negative charges at the other end. By successively compressing and stretching the crystal at an appropriate frequency, an alternating electrical current is generated that can be converted into mechanical energy-specifically, ultrasonic waves. Scientists use different shapes and materials (including quartz and varieties of ceramic) in fashioning piezoelectric crystals: for instance, a concave shape is best for an ultrasonic wave that will be focused on a very tight point.

Piezoelectric transducers have a variety of applications in ultrasonic technology, and are capable of acting as receivers for ultrasonic vibrations. Some of the simplest ultrasonic applications build on the fact that the upper range of audibility for human beings tens relatively low among animals.

Cats, by comparison, have an infrasound threshold only slightly higher than that of humans (100 Hz), but their ultrasound range of audibility is much greater-32,000 Hz instead of a mere 20,000. This explains why a cat sometimes seems to respond mysteriously to noises its owner is incapable of hearing. For dogs, the difference is even more remarkable: their lower threshold is 40 Hz, and their high end 46,000 Hz, giving them a range more than twice that of humans.

On a more practical level, a dog whistle is foto teens extremely simple ultrasonic or near-ultrasonic teenz, one that obviously foto teens no transducers. In fact, the Acme Silent Dog Whistle, which the company has produced since 1935, emits a tone that humans can hear (the listed range is 5,800 to foto teens Hz), but which dogs can hear much better.

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Comments:

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