Ultrasonic

a term used to describe sound waves that are inaudible to humans as they have a frequency above 20kHz. Although the human ear is incapable of detecting such a high FREQUENCY, some animals, such as dogs and bats, can detect ultrasonic waves (also known as ultrasound). Ultrasound is used wisely in industry, medicine and research. For example, it is used to detect faults or cracks in underground pipes and to destroy kidney stones and gallstones. The most recent development in ultrasonics is their use in chemical processes to trigger reactions involved in the production of food, plastics and antibiotics. Ultrasonics make certain chemical processes safer and cheaper as they eliminate the need for high temperatures and expensive catalysts.

Taken from Dictionary of Science

Occlusion

is when warm and cold air meet in a DEPRESSION, where the warm air is lifted above the colder air.

Taken from Dictionary of Science

Mach number

the speed of a body expressed as a ratio with the SPEED OF SOUND. Mach I is sonic speed, and thus below I is subsonic and above I is supersonic.

Taken from Dictionary of Science

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Mach number (Ma or M) (generally pronounced /ˈmɑːk/, sometimes /ˈmɑːx/ or /ˈmæk/) is the speed of an object moving through air, or any fluid substance, divided by the speed of sound as it is in that substance. It is commonly used to represent an object's (such as an aircraft or missile) speed, when it is travelling at (or at multiples of) the speed of sound.

where

is the Mach number

is the speed of the source (the object relative to the medium) and

is the speed of sound in the medium