Every fact in the three sound lessons is listed here with where it comes from. The numbers in [brackets] on the lesson pages link to this list.
Wikipedia was not used as a source. Numbers are rounded (for example 9.8 m/s² for Earth's gravity). The text was drafted with help from AI (Claude) and then checked against these sources. Corrections: hello@echoesof.science.
Where the numbers are less certain: the Krakatoa figures (heard about 4,800 km away, a pressure spike equal to about 172 dB at 160 km, the pressure wave going round the Earth several times) come from records collected after 1883 by the Royal Society and are retold in source [4]. The 172 dB value is a modern conversion of a barometer reading, so treat it as an estimate.
Type: Peer-reviewed open textbook
Defines sound as a disturbance of matter transmitted outward from its source, made of compressions and rarefactions, and explains that these make the eardrum vibrate.
Used in: Ages 10–11 (experiment); Ages 10–11 (quiz); Ages 10–11 (text); Ages 15–16 (text); Ages 6–7 (experiment); Ages 6–7 (quiz); Ages 6–7 (text)
https://openstax.org/books/college-physics-2e/pages/17-1-sound
Type: Peer-reviewed open textbook
Gives v = f·λ, the speed of sound in air (343 m/s at 20 °C), its temperature dependence v = 331 m/s·√(T/273 K), speeds in water (1480 m/s) and steel (5960 m/s), and the audible range of 20 to 20,000 Hz.
Used in: Ages 10–11 (experiment); Ages 10–11 (quiz); Ages 10–11 (text); Ages 15–16 (experiment); Ages 15–16 (quiz); Ages 15–16 (text)
https://openstax.org/books/college-physics-2e/pages/17-2-speed-of-sound-frequency-and-wavelength
Type: Peer-reviewed open textbook
Defines the decibel scale β = 10·log₁₀(I/I₀) with I₀ = 10⁻¹² W/m², and gives typical levels: whisper 20 dB, conversation 60 dB, rock concert and threshold of pain 120 dB, jet at 30 m 140 dB, bursting of eardrums 160 dB, with exposure times for damage.
Used in: Ages 10–11 (quiz); Ages 10–11 (text); Ages 15–16 (quiz); Ages 15–16 (text); Ages 6–7 (quiz); Ages 6–7 (text)
https://openstax.org/books/college-physics-ap-courses-2e/pages/17-3-sound-intensity-and-sound-level
Type: Science magazine, retelling historical records
Retells the 1883 records: the eruption was heard on Rodrigues about 3,000 miles (4,800 km) away; a barometer at the Batavia gasworks about 100 miles (160 km) away jumped by over 2.5 inches of mercury (over 172 dB); the pressure wave went round the globe three to four times in each direction; the captain of the Norham Castle, 40 miles away, wrote that the eardrums of over half his crew were shattered.
Used in: Ages 10–11 (text); Ages 15–16 (quiz); Ages 15–16 (text); Ages 6–7 (quiz); Ages 6–7 (text)
https://nautil.us/the-sound-so-loud-that-it-circled-the-earth-four-times-235101/
Type: Space agency
Explains that most of space is essentially a vacuum, with no medium for sound waves to travel through. Also notes that gas in galaxy clusters can carry sound waves.
Used in: Ages 10–11 (quiz); Ages 10–11 (text); Ages 15–16 (quiz); Ages 15–16 (text); Ages 6–7 (quiz); Ages 6–7 (text)
https://science.nasa.gov/learners/highlights/data-sonifications