Sonic boom the ground. For example, the speed of sound at is about , but an aircraft must travel at least (Mach 1.12, where Mach 1 equals the speed of sound) for a boom to be heard on the ground. The composition of the atmosphere is also a factor. Temperature variations, humidity, atmospheric pollution, and winds can all have an effect on how a sonic boom is perceived on the ground. Even the ground itself can influence the sound of a sonic boom. Hard surfaces such as concrete, pavement, and large buildings can cause reflections which may amplify the sound of a
Speed of sound the corresponding seismic waves are called P-waves (primary waves) and S-waves (secondary waves), respectively. The sound velocities of these two types of waves propagating in a homogeneous 3-dimensional solid are respectively given by where The last quantity is not an independent one, as . Note that the speed of pressure waves depends both on the pressure and shear resistance properties of the material, while the speed of shear waves depends on the shear properties only. Typically, pressure waves travel faster in materials than do shear waves, and in earthquakes this is the reason that the onset of an earthquake is