S-waves cannot be supported by the liquid core, producing shadow regions. Both waves travel at different speeds in the different regions of Earth, but in general, P-waves travel faster than S-waves. Because S-waves do not pass through the liquid core, two shadow regions are produced ( Figure 17.11).įigure 17.11 Earthquakes produce both longitudinal waves (P-waves) and transverse waves (S-waves), and these travel at different speeds. The time between the P- and S-waves is routinely used to determine the distance to their source, the epicenter of the earthquake.

The P-wave gets progressively farther ahead of the S-wave as they travel through Earth’s crust. P-waves have speeds of 4 to 7 km/s, and S-waves range in speed from 2 to 5 km/s, both being faster in more rigid material. Both types of earthquake waves travel slower in less rigid material, such as sediments. For that reason, the speed of longitudinal or pressure waves (P-waves) in earthquakes in granite is significantly higher than the speed of transverse or shear waves (S-waves). The bulk modulus of granite is greater than its shear modulus. Earthquakes produce both longitudinal and transverse waves, and these travel at different speeds. Seismic waves, which are essentially sound waves in Earth’s crust produced by earthquakes, are an interesting example of how the speed of sound depends on the rigidity of the medium. Explain why this is so.Īlthough sound waves in a fluid are longitudinal, sound waves in a solid travel both as longitudinal waves and transverse waves. However, you see the other shell for several milliseconds before you hear the explosion. You hear the explosion of one as soon as you see it. Imagine you observe two firework shells explode. Differentiating with respect to the density, the equation becomes Taking the natural logarithm of both sides yields ln p − γ ln ρ = constant. The number of moles and the molar mass are constant and can be absorbed into the constant p ( 1 ρ ) γ = constant. The density equals the number of moles times the molar mass divided by the volume, so the volume is equal to V = n M ρ. Adiabatic processes are covered in detail in The First Law of Thermodynamics, but for now it is sufficient to say that for an adiabatic process, p V γ = constant, p V γ = constant, where p is the pressure, V is the volume, and gamma ( γ ) ( γ ) is a constant that depends on the gas. A process where heat is not added or removed from the system is known as an adiabatic system. During the process of compression and expansion of the gas, no heat is added or removed from the system.

Ĭonsider a sound wave moving through air. ρ v d v = − d p ( − v d ρ ) v = − d p v = d p d ρ. Ρ v d v = − d p ( − v d ρ ) v = − d p v = d p d ρ.

Soundwaves background