Ground vibration boom Ground vibration boom Ground vibration boom is a phenomenon of very large increase in ground vibrations generated by high-speed railway trains travelling at speeds higher than the velocity of Rayleigh surface waves in the supporting ground. This phenomenon, which is similar to a sonic boom from supersonic aircraft, was theoretically predicted in 1994. Its first experimental observation took place in 1997-1998 on the newly built high-speed railway line in Sweden (from Gothenburg to Malmo) for high-speed trains X 2000. At some locations along this line characterised by very soft ground (near Ledsgard) the Rayleigh wave velocity was as low as
Speed of sound speed of sound of a monatomic gas goes up by a factor of This gives the 9% difference, and would be a typical ratio for speeds of sound at room temperature in helium vs. deuterium, each with a molecular weight of 4. Sound travels faster in helium than deuterium because adiabatic compression heats helium more since the helium molecules can store heat energy from compression only in translation, but not rotation. Thus helium molecules (monatomic molecules) travel faster in a sound wave and transmit sound faster. (Sound travels at about 70% of the mean molecular speed in gases; the figure