Ultrasound is ultra high frequency sound waves which are beyond the upper threshold of hearing for humans which is a frequency of 20 000 Hz.
Ultra sound is partially relected when it meets a boundary between two different materials (or material of different densities).
This is used in medical applications like;
- prenatal scanning
- imaging ligaments, muscles & kidneys
- the removal of kidney stones
The time taken for reflections to reach the ultrasound detector can be used to determine how far away the boundary is.
distance = speed x time
(metres, m) (metres per second, m/s) ( seconds, s)