Complete each stage to unlock the next one.
Astronauts on a spacewalk have to use radios to talk to each other — even when their helmets are almost touching. Meanwhile, you can hear a whale song underwater from kilometres away. And a bat navigates a pitch-black cave without touching anything. All of this is sound — but what makes some sounds travel so far, and others not at all?
Astronauts on a spacewalk have to use radios to talk to each other — even when their helmets are almost touching. Meanwhile, you can hear a whale song underwater from kilometres away. And a bat navigates a pitch-black cave without touching anything. All of this is sound — but what makes some sounds travel so far, and others not at all?
Sound is picky: it needs matter to exist. It can't cross even a millimetre of vacuum. But when it has a medium, it can travel through rock at 6000 m/s, through water at 1500 m/s, and through air at 343 m/s — each medium has a completely different speed. Understanding why unlocks everything from echolocation to earthquake seismology.
Sound is a longitudinal mechanical wave — particles vibrate parallel to the direction of travel, creating compressions and rarefactions. It requires a medium (solid, liquid, or gas) and cannot travel through vacuum. Speed increases with medium density and elasticity.
Sound travels at 343 m/s in air at 20°C, about 1480 m/s in water, and about 5000–6000 m/s in steel. The denser and more rigid the medium, the faster sound travels — because the restoring forces between particles are stronger. Frequency determines pitch; amplitude determines loudness (volume). The decibel scale measures sound intensity. Humans hear 20 Hz–20,000 Hz; dogs up to 65,000 Hz; bats use 20,000–200,000 Hz for echolocation, getting detail as fine as a few millimetres.