section_path: Physics/Speed
section_name: Speed
paragraph_text: Speed
  
  The speed of sound depends on the medium the waves pass through, and is a fundamental property of the material. The first significant effort towards measurement of the speed of sound was made by Isaac Newton. He believed the speed of sound in a particular substance was equal to the square root of the pressure acting on it divided by its density:
  
  This was later proven wrong and the French mathematician Laplace corrected the formula by deducing that the phenomenon of sound travelling is not isothermal, as believed by Newton, but adiabatic. He added another factor to the equation— gamma —and multiplied γ {\displaystyle {\sqrt {\gamma }}} by p / ρ {\displaystyle {\sqrt {p/\rho }}},thus coming up with the equation c = γ ⋅ p / ρ {\displaystyle c={\sqrt {\gamma \cdot p/\rho }}}.Since K = γ ⋅ p {\displaystyle K=\gamma \cdot p},the final equation came up to be c = K / ρ {\displaystyle c={\sqrt {K/\rho }}},which is also known as the Newton–Laplace equation. In this equation, K is the elastic bulk modulus, c is the velocity of sound, and ρ {\displaystyle \rho } is the density. Thus, the speed of sound is proportional to the square root of the ratio of the bulk modulus of the medium to its density.
  
  Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in gases depends on temperature. In 20 °C (68 °F) air at sea level, the speed of sound is approximately 343 m/s (1,230 km/h; 767 mph) using the formula v = 331 + 0.6 T. The speed of sound is also slightly sensitive, being subject to a second-order anharmonic effect, to the sound amplitude, which means there are non-linear propagation effects, such as the production of harmonics and mixed tones not present in the original sound (see parametric array). If relativistic effects are important, the speed of sound is calculated from the relativistic Euler equations.
  
  In fresh water the speed of sound is approximately 1,482 m/s (5,335 km/h; 3,315 mph). In steel, the speed of sound is about 5,960 m/s (21,460 km/h; 13,330 mph). Sound moves the fastest in solid atomic hydrogen at about 36,000 m/s (129,600 km/h; 80,530 mph).