Military fighter jets are capable travelling at speeds faster than the speed of sound. This critical speed of approximately 1,225km/h is known as Mach 1 - exceeding Mach 1 is known as going supersonic.
Sonic booms do not always occur when aircraft fly at supersonic speeds. A sonic boom is created when aircraft travel at approximately 1,225km/h at sea level and the temperature is 20C. Sonic booms can travel some distance and the sound can be enhanced by certain weather conditions, such as high humidity and cloud cover.
In some cases, sonic booms can damage property, especially glass such as windows.
Supersonic flight is not permitted over land and is usually only practiced over the ocean, well away from the coast, however, noise from a sonic boom may travel and be heard over land areas.