Sound — Describe

What are the uses of ultrasound in non-destructive testing, medical scanning and sonar, and how can it be used to calculate depth or distance?

Ultrasound (sound waves of frequency above 20000 Hz) is used in non-destructive testing to detect cracks or flaws inside materials without damaging them, in medical scanning to produce images of soft tissue (e.g. prenatal scans) without the risks associated with ionising radiation, and in sonar to measure water depth or locate underwater objects. In sonar, a pulse of ultrasound is emitted and the time for its echo to return is measured; since the pulse travels to the object and back, distance = (speed × time) / 2.