SUPPLEMENTARY TEXT:
Supersonics and Ultrasonic
You may have heard the sonic thunder, or sudden sharp bang that occurs when a plane is flying faster than sound. How does the bang arise? The speed of sound is about 750 miles an hour. So long as an airplane is flying well below the speed of sound, the particles of air move out of the way fast enough. The plane nearing the speed of sound, the air can not move out of the way fast enough. It is, therefore, thrown suddenly aside, forming a shock wave.
The shock waves from the plane spread out until they reach our ears and give us the sound we call a” sonic bang”. It is these waves from waves that may damage the windows on the ground when a supersonic plane flies overhead. The term supersonic applies to motion at a velocity greater than that of sound.
Ultrasonic, on the other hand, is something quite different. It is the study of sound waves whose frequency is too high for us to hear.
An ultrasonic wave is reflected as an echo by an object. By measuring the time it takes the wave to travel to the object and return back, we can find out exactly how far away the object is. This is how sound is used to measure the depth of the sea. In the same manner, bats avoid obstacles with remarkable accuracy by emitting high frequency cries and timing their echo return.
Ultrasonic waves have many uses. We can use them, instance, to measure the thickness of metal or to detect flaws in it.
Another use of ultrasonic is to set up vibrations in liquids to clean tiny instrument parts like watch springs. A lot of other applications, such as drilling, welding, cutting, etc. make ultrasonic a very useful tool to be used in industry, science and medicine.
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