---
title: Thunder, sirens and how fast sound travels — how Mova does on the tests · Physics
description: Lesson 18 of the physics course of Mova's primary school: 6 of 11 tests right, exam 2 of 4, every question with the options, the student's choice, the right answer and why it chose.
---

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# Thunder, sirens and how fast sound travels

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**Tests:** 6 of 11 right · **Exam:** 2 of 4 right · **Kind:** ★ · **Understood:** 10 of 15 · **Run:** 2026-10-18, commit `f3c23ea72`

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Lesson 18 of the physics course of Mova's primary school, as Mova's small model took its tests: it had read this lesson and the ones before it and learned from their exercises. Each test shows the options in the order the student saw them, its choice, the right answer, the score of every option and why it chose. The lesson itself, sentence by sentence with trees and pragmatics: [the lesson in the corpora](https://md.mova.elamur.ai/free/en/corpora/school/physics/18-thunder-sirens-and-how-fast-sound-travels/).

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Every question of this lesson and each of its options parsed by Mova, with trees and pragmatics: [the lesson's questions in the corpora](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/).

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### Test 1 · ★ · wrong ✗ {#t1}

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no worries, thunder's like 20 seconds after the flash, storm's miles off yeah?

- **1.** No, it means the storm is right overhead — no support
- **2.** Yes, 20 seconds means hundreds of kilometres — **← Mova's choice** · score 4
- **3.** No, that is only about seven kilometres, still close enough to be careful — **✓ the right answer** · no support
- **4.** Yes, thunder after 5 seconds is safe — no support

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**Why:** It took the question to ask which statement is true. It chose option 2 with score 4, the only option with support. Its support: lesson 18, line 2: «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.», reached through the remembered sentence the question matched. What matched: the same action «mean» (+3); the same doer «three seconds» (+1). The right option, 3, found no support in what it remembers. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/t1/)

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### Test 2 · ★ · wrong ✗ {#t2}

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A cartoon shows thunder and lightning arriving together, even from far away. What is wrong?

- **1.** Lightning makes no light far away — **← Mova's choice** · no support
- **2.** Far away, the thunder comes later than the flash — **✓ the right answer** · no support
- **3.** Nothing, they always arrive together — no support
- **4.** Thunder always comes before the flash, however far away — no support

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**Why:** No option found support in what it remembers, so it guessed: it took the first option shown. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/t2/)

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### Test 3 · ★ · right ✓ {#t3}

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Why is putting your ear to a railway line a terrible idea in real life?

- **1.** Trains are faster and quieter than you think, and railways are deadly — **← Mova's choice** · **✓ the right answer** · score 2
- **2.** Steel carries no sound at all — no support
- **3.** It works only in old films — no support
- **4.** The rail would freeze your ear — no support

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**Why:** It took the question to ask why something happens (its cause). It chose option 1 with score 2, the only option with support. Its support: lesson 18, line 11: «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 n…», reached through the same lesson line as the sentence the question matched. What matched: the same doer «trains» (+2). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/t3/)

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### Test 4 · ★ · wrong ✗ {#t4}

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A police car drives past you at speed. Which is true about its siren?

- **1.** It sounds the same the whole time — no support
- **2.** It sounds lower coming and higher going — **← Mova's choice** · score 2
- **3.** It sounds higher coming and lower going — **✓ the right answer** · no support
- **4.** It goes silent as it passes — no support

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**Why:** It took the question to ask which statement is true. It chose option 2 with score 2, the only option with support. Its support: lesson 17, line 10: «Short, thin, tight strings wobble fast and sound high; long, thick, slack strings wobble slowly and sound low; blowing across bottles with different amounts of…», reached through the same lesson line as the sentence the question matched. What matched: the same action «sound» (+2); the same property (+1). Against it: a different doer (counts against) (-1). The right option, 3, found no support in what it remembers. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/t4/)

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### Test 5 · ★ · right ✓ {#t5}

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Why do foxes and rabbits have big ears that turn?

- **1.** Big ears are only there for showing off to others — no support
- **2.** Big ears help them to run along much faster — no support
- **3.** Big ears keep them warm out in the cold snow — no support
- **4.** They gather more sound from where it comes — **← Mova's choice** · **✓ the right answer** · score 8

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**Why:** It took the question to ask why something happens (its cause). It chose option 4 with score 8, the only option with support. Its support: lesson 18, line 16: «Cupping your hand behind your ear gathers more sound into it, which is why foxes and rabbits have big ears that turn towards sounds.», reached through the same lesson line as the sentence the question matched. What matched: the same action «gather» (+5); the same thing acted on «more sound» (+3). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/t5/)

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### Test 6 · ★ · right ✓ {#t6}

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ugh my voice on the video sounds well weird, is the phone broken?

- **1.** Yes, phones always change voices — no support
- **2.** No, your voice changes when you hear it back — no support
- **3.** No, that is how you really sound to others — **← Mova's choice** · **✓ the right answer** · score 7
- **4.** Yes, your voice is deeper than that — score 1

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**Why:** It took the question to ask which statement is true. It chose option 3 with score 7, against 1 for the next best. Its support: lesson 18, line 14: «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…», reached through the remembered sentence the question matched. What matched: the same circumstance (+5); the same action «sound» (+3). Against it: a different doer (counts against) (-1). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/t6/)

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### Test 7 · ★ · right ✓ {#t7}

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What would a stretched-out slack string do to your string telephone?

- **1.** Make your friend hear you a little sooner — no support
- **2.** Carry the sound badly or not at all — **← Mova's choice** · **✓ the right answer** · score 6
- **3.** Make all the sounds come out much higher — no support
- **4.** Carry the sound twice as well as before — score 6

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**Why:** It took the question to ask what is done. It chose option 2 with score 6, tied with another option at 6 (the first shown, or the one claiming less beyond what it knows, wins). Its support: lesson 18, line 12: «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.», reached through the remembered sentence the question matched. What matched: it fills the role the question asks for (+6); the same action «carry» (+4). Against it: a different doer (counts against) (-2); a different thing acted on (counts against) (-2). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/t7/)

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### Test 8 · ★ · right ✓ {#t8}

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A whip makes a sharp crack. What is happening at its tip?

- **1.** The leather at the very end snaps in two with a crack — no support
- **2.** The tip of the whip hits a fly that is passing by — no support
- **3.** It moves faster than sound and makes a tiny boom — **← Mova's choice** · **✓ the right answer** · score 2
- **4.** The handle makes the crack, and the tip makes nothing — no support

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**Why:** It took the question to ask which statement is true. It chose option 3 with score 2, the only option with support. Its support: lesson 18, line 13: «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.», reached through the remembered sentence the question matched. What matched: the same action «make» (+3); the same doer «cracking whip» (+1). Against it: a different thing acted on (counts against) (-2). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/t8/)

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### Test 9 · ★ · wrong ✗ {#t9}

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The same whisper is heard on the far side of a round gallery but not across a square hall. Why?

- **1.** Whispers travel faster in round rooms — **← Mova's choice** · score 3
- **2.** Round rooms make every sound louder by a kind of magic — no support
- **3.** The curved wall guides the sound round its edge — **✓ the right answer** · no support
- **4.** Square halls block all whispers — no support

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**Why:** It took the question to ask why something happens (its cause). It chose option 1 with score 3, the only option with support. Its support: lesson 18, line 17: «A whisper can travel round a curved wall in a whispering gallery, such as the famous one in St Paul's Cathedral in London.», reached through the option's own match among the sentences about the question's things. What matched: the same action «travel» (+2); the same doer «whisper» (+1). The right option, 3, found no support in what it remembers. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/t9/)

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### Test 10 · ★ · wrong ✗ {#t10}

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Which is true about sound and light?

- **1.** They travel at exactly the same speed through the air — **← Mova's choice** · score 9
- **2.** Light is about a million times faster than sound — **✓ the right answer** · score 1
- **3.** Sound is a kind of light — no support
- **4.** Sound is faster than light — score 6

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**Why:** It took the question to ask which statement is true. It chose option 1 with score 9, against 6 for the next best. Its support: lesson 18, line 11: «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 n…», reached through the remembered sentence the question matched. What matched: the same circumstance (+5); the same action «travel» (+3); the same doer «sound» (+1). The right option, 2, scored 1. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/t10/)

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### Test 11 · ★ · right ✓ {#t11}

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Astronomers use the same squashed and stretched waves with light from stars. What can they learn?

- **1.** How many planets each star has — no support
- **2.** How fast the stars are moving towards or away from us — **← Mova's choice** · **✓ the right answer** · score 5
- **3.** How hot the stars are inside — no support
- **4.** How old the stars are — no support

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**Why:** It took the question to ask what it is done to. It chose option 2 with score 5, the only option with support. Its support: lesson 18, line 10: «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…», reached through the same lesson line as the sentence the question matched. What matched: the same action «move» (+2); the same doer «star» (+2); the same property (+1). · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/t11/)

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### Exam question 1 · formal language · wrong ✗ {#e1}

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Identify the principal reason for which thunder is perceived subsequent to the corresponding flash of lightning.

- **1.** The thunder is produced after the lightning has ceased — **← Mova's choice** · no support
- **2.** The lightning and the thunder originate in different clouds — no support
- **3.** The ear responds more slowly than the eye — no support
- **4.** Light is propagated at a vastly greater speed than sound — **✓ the right answer** · no support

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**Why:** No option found support in what it remembers, so it guessed: it took the first option shown. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/e1/)

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### Exam question 2 · formal language · wrong ✗ {#e2}

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It is given that an interval of nine seconds elapses between a flash and the ensuing thunder. Ascertain the approximate distance of the discharge.

- **1.** Nine kilometres — **← Mova's choice** · no support
- **2.** Twenty-seven kilometres — no support
- **3.** One kilometre — no support
- **4.** Three kilometres — **✓ the right answer** · no support

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**Why:** No option found support in what it remembers, so it guessed: it took the first option shown. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/e2/)

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### Exam question 3 · formal language · right ✓ {#e3}

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Which of the following statements most accurately characterises the alteration of the pitch of a passing siren?

- **1.** The pitch rises upon approach and falls upon recession — **← Mova's choice** · **✓ the right answer** · no support
- **2.** The pitch is determined solely by the volume — no support
- **3.** The pitch remains constant throughout — no support
- **4.** The pitch falls upon approach and rises upon recession — no support

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**Why:** No option found support in what it remembers, so it guessed: it took the first option shown. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/e3/)

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### Exam question 4 · formal language · right ✓ {#e4}

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State the anticipated consequence of prolonged exposure to sound of excessive intensity.

- **1.** Permanent damage to the sensory hairs of the inner ear — **← Mova's choice** · **✓ the right answer** · no support
- **2.** An enhancement of the acuity of hearing — no support
- **3.** No consequence of any description — no support
- **4.** An enlargement of the external ear — no support

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**Why:** No option found support in what it remembers, so it guessed: it took the first option shown. · [the question and its options parsed, with trees and pragmatics](https://md.mova.elamur.ai/free/en/corpora/questions/physics/18-thunder-sirens-and-how-fast-sound-travels/e4/)

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- ← previous: [17. What sound is: wobbles in the air](https://md.mova.elamur.ai/free/en/school-run/physics/17-what-sound-is-wobbles-in-the-air/)
- next →: [19. Bangs and loud sounds: firecrackers and ears](https://md.mova.elamur.ai/free/en/school-run/physics/19-bangs-and-loud-sounds-firecrackers-and-ears/)
- ↑ back to [Physics](https://md.mova.elamur.ai/free/en/school-run/physics/)