(i) SONAR, which stands for Sound Navigation and Ranging, utilizes the reflection of sound to measure the speed and distance of underwater objects.
(ii) The functioning of a stethoscope involves multiple reflections of sound, allowing the sound of a patient's heartbeat to reach the doctor's ear.
(i) The kind of person the doctor is (money, possessions)
(ii) The kind of person he wants to be (appearance, ambition)
ABCD is a quadrilateral in which AD = BC and ∠ DAB = ∠ CBA (see Fig. 7.17). Prove that
(i) ∆ ABD ≅ ∆ BAC
(ii) BD = AC
(iii) ∠ ABD = ∠ BAC.

Sound is a vibration that propagates the mechanical wave of displacement and pressure, through a medium can be of any matter. In other words, the sound is the thin line between Music sound and Noise.
Sound can be divided into two types depending on its frequency. The following are:-