Ultrasonic sound waves are a movement of particles back and forth along the direction the sound travels. Ultrasound is used in many applications. It is used in sonar for locating and measuring objects underwater.
Ultrasonic sound waves can also be used in medicine. For example examining the brain of an ill person or to examine a fetus (unborn baby) in the mother's womb, avoiding the use of X-ray which is far more harmful.
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