{ "items" : [
    { "id" : "http://dbpedia.org/resource/Speed_of_sound"
      "properties" : {
        "http://www.w3.org/2000/01/rdf-schema#comment" : [ "The speed of sound is the distance travelled per unit time by a sound wave propagating through an elastic medium. The SI unit of the speed of sound is the metre per second (m/s). In dry air at 20 °C, the speed of sound is 343.2 metres per second (1,126 ft/s). This is 1,236 kilometres per hour (768 mph; 667 kn), or a kilometre in 2.914 s or a mile in 4.689 s. The speed of sound in an ideal gas is independent of frequency, but does vary slightly with frequency in a real gas."] } } }
