Properties of a Wave

II. Fill in the gaps with the terms given to you: pitch, amplitude, period, wavelength, frequency.

A number of properties are commonly used to define a wave. The 1 _____ may be defined as the horizontal distance between two successive equivalent points on the waveform. For convenience, these two points are usually taken at peaks (highest point) or troughs (lowest). The 2 _____ then is the time it takes for the wave to complete one full cycle.

The 3 ______ equates to the height of the wave; loud sounds produce waves of higher amplitude. The loudness or intensity of sound is measured in decibels; however, it must be remembered that this is not a linear or absolute scale of measurement. The lowest threshold of human hearing is set at zero; a decibel is sometimes defined as the smallest change in volume discernable by a human. For a doubling in volume, the decibel level goes up by six. Within this scale, normal speech levels fit in at around 60dB.

The frequency of a wave is the number of cycles that pass a set point in a second, and is measured in Hertz (Hz). Frequency is intimately connected to _____, although they are not exactly synonymous; the A above middle C is a vibration at a rate of 440 Hz. Lower frequency vibrations are perceived as being lower in pitch, and higher frequencies seem higher in pitch.

III. Discussion:

1. How can you characterize the language of these paragraphs? Is it totally scientific? Explain your viewpoint. Think where this article could be published.

2. Who might need this information and for what purpose?

3. Who else might want to use the information about sound and hearing?

4. Give a scientific definition of sound. What substances can it travel through? What properties are used to define a wave?

5. What is interference? In what conditions is it called constructive? When does destructive interference occur?

6. How are the terms “condensation”, “rarefaction”, “frequency”, “beats”, “amplitude”, “interference” connected?

7. What happens when two sound waves with different frequencies overlap? How do musicians know if their instruments are out of tune?

8. Explain the properties of sound for: A. A student in medicine: B. A radio journalist; C. A sound recording company assistant; D. A biologist studying the flight of a bat.

Text IX

Infrasound at the Ghost-Busters' Service

I Put the paragraphs in the right order:

A. Infrasound is very surprising by itself. For many years seamen were pondering over the mystery of "flying Dutchmen", ships that wandered around the seas without crews on board. The ships were in good repair, but there were no people on board at all. Where have they gone? Well-known vessel Mary Celeste was the last of such ships; that was a wonderful schooner noticed by some other vessel in the ocean. When the vessel approached Mary Celeste and its seamen entered the schooner, they were astonished to find hot dinner and entries recently made by the captain in the ship journal. There were absolutely no people on board of Mary Celeste. They disappeared but no traces could be found.

B. "Some invisible hand" might have been suggested as a probable explanation of the phenomenon by ordinary people but not by a scientist. That is why Vick Tandy suddenly arrived at a conclusion that the moving of the blade was resonance oscillations caused with sound waves. This is just exactly the same when we hear tea services clink in a buffet when music is thundering in the room. But in fact, it was actually very quiet in the laboratory. To be sure, Vick Tandy measured the sound in the laboratory with special apparatuses. He was surprised to see that the sound in the room was unimaginable; the sound waves were very low, although the scientist couldn't hear them. That was infrasound. It took the scientist a lot of time to find out the source of the infrasound; it was emitted by a recently set ventilator in the air conditioner. As soon as the air conditioner was switched off, the blade stopped vibrating. C. Soon Vick Tandy managed to discover the factors quite accidentally. Vick's hobby, fencing helped him with it. Some time after the scientist saw the "ghost" he brought his rapier to the laboratory to set it right before a forthcoming fencing tournament. Suddenly Vick felt the blade gripped in a vice started vibrating more and more as if some invisible hand touched it. D. Computer specialist Vick Tandy from Coventry University always considered all legends about ghosts a nonsense and never took them seriously. Once he traditionally spent his evening working in a laboratory when he suddenly broke into a cold sweat. Vick felt somebody was watching him with sinister eyes. Then the sinister something assumed a gray material form, crossed the room and approached the scientist. In the vague outline Vick could discern legs, arms and fog where the figure must have a head; there was a dark spot in the center of the fog which might be a mouth. In an instance, the vision disappeared in the air without leaving a trace. E. The mystery was unsolved for decades, until it became clear that infrasound was the explanation of the phenomenon. As it turned out, infrasound of seven hertz emitted by ocean waves under some definite conditions was the reason of it. But infrasound of seven hertz is terrible for people: they may go mad and throw themselves overboard to save their lives.

F. As soon as Vick Tandy recovered after the first fear and shock he started doing

as a scientist: he started looking for the cause of the unusual phenomenon. Hallucinations might have been the easiest way to explain the phenomenon. On the other hand, Vick didn't use drugs, was moderate in drinking alcohol and coffee. As for weird forces, the scientist strongly disregarded them. So, Vick Tandy decided to look for ordinary physical factors that might explain the phenomenon.

II Fill in the gaps in the extract below: natural, phenomena, frequency, air drag, question, resonating, measured, low.

Vick Tandy supposed that his night vision might be connected with infrasound as well. When he A._____ the infrasound in the laboratory, the showing was 18.98 hertz, just exactly the B. ______ under which a human eyeball starts C. _____. So, to all appearances sound waves made Vick Tandy's eyeballs resonate and produced an optical illusion: he saw a figure that didn't exist in fact. Further investigation of the phenomenon revealed that sound waves of this D._____ frequency may appear rather frequently under E.____ conditions. Infrasound arises when strong gusts of wind clash with chimneys or towers. These heavy basses penetrate even through very thick walls. Such sound waves start rumbling in tunnel-shaped corridors. This is the reason why people often come across ghosts in long serpentine corridors of ancient castles looking like tunnels. Strong winds are quite typical of Great Britain. Vick Tandy published the results of his research in the magazine of the Society of Physical Researches. The Society was formed in 1822 to unite British parapsychologists and naturalists; the Society is working to find reasonable explanations to paranormal phenomena. This is quite understandable that professional "ghost busters" got enthusiastic with Tandy's idea. Leading parapsychologists of Great Britain think this idea will help give explanations to many of mysterious D.______. However, other scientists call the idea into E._____. Physicists studying effect of infrasound upon the human body say that volunteers participating in their experiments complain of weariness, high pressure in the eyes and in the ears, but never mention hallucinations or ghosts. At that, physicists say that drivers also have no optical illusions when cars overcome the F.____ at a really high speed and the level of infrasound waves is very high. http://www.oocities.com/hauntpursuit/infrasound1.html