--- title: Thunder, sirens and how fast sound travels — a lesson of Mova's school · trees and pragmatics description: «Thunder, sirens and how fast sound travels», a lesson of the physics course of Mova's primary school, sentence by sentence with dependency trees and pragmatics. It begins: Sound is fast, but nowhere near as fast as light: in air it goes about one kilometre every three seconds, while light crosses t --- [Mova](https://md.mova.elamur.ai/free/en/) · [this page in HTML](https://mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/) [home](https://md.mova.elamur.ai/free/en/) / [corpora](https://md.mova.elamur.ai/free/en/corpora/) / [school](https://md.mova.elamur.ai/free/en/corpora/school/) / [Physics](https://md.mova.elamur.ai/free/en/corpora/school/physics/) / Thunder, sirens and how fast sound tra… # Thunder, sirens and how fast sound travels Lesson 18 of the physics course of Mova's primary school: 17 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: [the lesson at school](https://md.mova.elamur.ai/free/en/school-run/physics/18-thunder-sirens-and-how-fast-sound-travels/). - [0](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/0/) — Sound is fast, but nowhere near as fast as light: in air it goes about one kilometre every three seconds, while light crosses the same distance almost instantly. - [1](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/1/) — That is why you see the flash of lightning first and hear the thunder later; every three seconds of waiting means the storm is about a kilometre away. - [2](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/2/) — Sound moves much faster through solid things like steel or a tight string than through air, because their tightly packed bits pass the wobble on quickly. - [3](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/3/) — When an ambulance races towards you its sound waves are squashed together and the siren sounds higher; as it drives away they are stretched out and it sounds lower. - [4](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/4/) — Loud low sounds are big pushes of air, so at a concert you can feel the drums in your chest, and very loud music for a long time can damage your ears for ever. - [5](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/5/) — In air sound travels about one kilometre every three seconds, while light arrives almost instantly, being about a million times faster. - [6](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/6/) — Counting the seconds between lightning and thunder and dividing by three gives roughly how many kilometres away the storm is. - [7](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/7/) — Lightning heats the air in an instant to hotter than the surface of the Sun, and the air bursts outwards with a huge sound wave, the thunder. - [8](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/8/) — Thunder rumbles because sound from different parts of the long lightning bolt reaches you at different times. - [9](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/9/) — A siren sounds higher as it comes towards you and lower as it goes away, because its waves are squashed in front and stretched out behind; astronomers use the same squashing and stretching of starlight to tell how fast a star moves towards or away from us. - [10](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/10/) — Sound travels many times faster in steel than in air, but railway lines are deadly, because trains come faster and more quietly than you expect, and you must never go on them. - [11](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/11/) — A string telephone works because a tight string carries the wobble from one cup to the other; a slack string or a finger on it stops the sound. - [12](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/12/) — A plane flying faster than sound piles its sound waves up into one big shock wave that is heard on the ground as a sonic boom; a cracking whip makes a tiny one. - [13](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/13/) — Your recorded voice sounds strange to you, though it is how others hear you, because you normally hear your voice partly through the bones of your head, which makes it sound deeper. - [14](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/14/) — Very loud sound for a long time damages the tiny hairs in your ears for ever, so people wear earplugs at loud concerts. - [15](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/15/) — Cupping your hand behind your ear gathers more sound into it, which is why foxes and rabbits have big ears that turn towards sounds. - [16](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/16/) — A whisper can travel round a curved wall in a whispering gallery, such as the famous one in St Paul's Cathedral in London. - ← previous: [What sound is: wobbles in the air](https://md.mova.elamur.ai/free/en/corpora/school/physics/17-what-sound-is-wobbles-in-the-air/) - next →: [Bangs and loud sounds: firecrackers and ears](https://md.mova.elamur.ai/free/en/corpora/school/physics/19-bangs-and-loud-sounds-firecrackers-and-ears/) - ↑ back to [Physics](https://md.mova.elamur.ai/free/en/corpora/school/physics/)