{"id":796,"date":"2026-08-12T11:20:30","date_gmt":"2026-08-12T11:20:30","guid":{"rendered":"https:\/\/physicsfundamentalsinfo.com\/blog\/?p=796"},"modified":"2026-08-24T13:03:42","modified_gmt":"2026-08-24T13:03:42","slug":"speed-of-sound","status":"publish","type":"post","link":"https:\/\/physicsfundamentalsinfo.com\/blog\/waves\/speed-of-sound\/","title":{"rendered":"The Speed of Sound (and What Changes It)"},"content":{"rendered":"\n
Definition<\/div>

\nThe speed of sound is the rate at which a pressure disturbance travels through a material, equal to about 343 m\/s in dry air at 20 \u00b0C. In a gas it is fixed by the temperature and by the gas itself, following v = sqrt(\u03b3RT\/M). Air pressure on its own does not change it.\n<\/p><\/div>\n\n

Count the seconds between a lightning flash and the thunder. Three seconds means the strike was roughly a kilometre away \u2014 a trick that works only because sound ambles along slowly enough to time with a wristwatch, while the light arrives essentially instantly.<\/p>\n\n

But that amble is not a fixed number. A trumpet plays sharp on a hot afternoon, an airliner cruising at 11 km hits Mach 1 far slower than it would at sea level, and a diver hears an outboard motor long before anyone at the surface does. Same physics \u2014 three different speeds.<\/p>\n\n

What Is the Speed of Sound?<\/h2>\n\n

The speed of sound is how fast a pressure wave travels through a material: about 343 m\/s in air at 20 \u00b0C, roughly 1,480 m\/s in fresh water, and around 5,000 m\/s along a steel rail.<\/p>\n\n

Here is the thing most people picture wrongly. Sound is not a packet of air flying from the speaker to your ear. Each molecule shuffles back and forth by a fraction of a millimetre and shoves its neighbour, which shoves its<\/em> neighbour \u2014 and the pattern<\/strong> of squeeze and stretch races away while the air itself stays put.<\/p>\n\n

Because that shuffling happens along the same line the wave travels, sound is a longitudinal wave<\/a> rather than the up-and-down ripple most diagrams of “a wave” show.<\/p>\n\n

\"Diagram<\/figure>\n\n

Sound moves as compressions and rarefactions. The air stays put; the pattern travels.<\/p>\n\n

So what sets the pace? Two properties fight it out in every material:<\/p>\n\n