The speed at which sound waves travel through a medium. All sound waves in fluids are longitudinal waves, and their speed c is given by c = (κ/ρ), where κ (kappa) is the bulk modulus of the fluid and ρ (rho) is its density. In the case of a gas, if we follow the equation of state for an ideal gas, c is given by c = ( RT γ/ M ). R is the gas constant, M is the molecular weight, T is the absolute temperature of the gas, and γ is the ratio of the specific heat at constant pressure to the specific heat at constant volume. Therefore, c is proportional to and does not depend on pressure. The speed of sound in air at temperature t °C is c = 331.5 + 0.6 t (m/sec) In most liquids, the speed of sound is between 1000 and 1500 meters per second, decreasing by 2 to 5 meters per second for every 1 degree Celsius rise. The speed of sound in water increases with temperature, reaching a maximum at 74°C. This is one of the many unusual properties of water caused by hydrogen bonds. In solids, in addition to the longitudinal waves found in air, there are two transverse waves. The speed of sound in solids depends on the state of the crystal and the direction of the crystal axis. In rubber, for example, it depends on the frequency, which is determined by the proportions of the mixture. In general, the speed of sound in solids decreases as temperature increases. [Yuichi Okuda] [Reference] | | |Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend |
音波が媒質中を伝わる速度。流体中の音波はすべて縦波であるが、その速度cは、流体の体積弾性率をκ(カッパ)、密度をρ(ロー)とするとc=(κ/ρ)で与えられる。気体の場合では、理想気体の状態方程式に従うとすると、c=(RTγ/M)で与えられる。Rは気体定数、Mは分子量、Tは気体の絶対温度、γは定圧比熱と定積比熱の比である。したがってcはに比例し、圧力にはよらない。温度t℃のときの空気中の音速は 液体の場合は、ほとんどの液体で音速は毎秒1000メートルから1500メートルであり、1℃上昇するに従い毎秒2~5メートル減少する。水中の音速は、温度とともに増加し、74℃で極大になる。これは水素結合がもたらす水の多くの異常物性の一つである。固体の場合には、空気中の場合のような縦波のほかに、二つの横波が存在する。固体中の音速は、結晶の状態、結晶軸の方向に依存する。ゴムなどでは、混合物の割合による振動数に依存する。一般に固体中では、温度が上がると音速は小さくなる。 [奥田雄一] [参照項目] | | |出典 小学館 日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について 情報 | 凡例 |
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