Fireworks are usually used for new-year celebration. Many types of fireworks are launched and explode in the sky. These things give us interesting performance. If we watch fireworks explode from far away, we will find that light from explosion and sound are not at the same time. This also happen when light storm blitz, its sound is left. These Phenomena is caused by the speed of sound and light is different. As we know that speed of sound is about 340 m/s, while light speed is 300.000 km/s. Since the speeds are known, so we can determine how far the distance from the fireworks to us is. It can be assumed that light from firework is seen at the same time when fireworks explodes and emits the sound because light speed is very high. Then after we watch fireworks explode, we can measure the time required until we hear the sound. The distance between us and fireworks is speed of sound multiplied by time (s=v x t).
Sound also can be used to determine the depth of sea. This system is called sonar system. Sonar system consists of transmitter and receiver. Function of transmitter is to produce sound in certain frequency. This sound will be reflected of by object (it can be coral reef or seabed). This reflected sound will be received by receiver. If the speed of sound in sea water is known, the depth of sea can be obtained.
Based on principle of sonar system, sound travels from transmitter to seabed and then it is reflected to the receiver. It means time required since sound is produced by transmitter until received by receiver is twice times of time needed of sound to reach seabed. So the deep of sea is half of time required multiplied by speed of sound in sea water (s = 0.5 x v x t).
The frequency used is ultrasonic, that is above the range of human hearing. The reason is because this frequency is inaudible. This frequency is shorter, so that the beam spread less and smaller objects can be detected.
