Echoes and ultrasound
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What this model shows
This model plays no sound. The speed of sound in air is taken as 340 m/s on the day; the wall is 100 m away.
The hand timings are chosen, not measured reactions: one timed echo starts 0.21 s late and stops 0.03 s late. The four timings of 20 intervals are chosen too; in one run the clapper lost the rhythm.
The single clap and the hand timing are slowed 10 times; the rhythm of 20 claps plays in real time; the three repeats and the voyage are sped up. The wavefronts show where the sound is, not its real shape.
Sea water is taken as 1500 m/s. The seabed is a fixed profile, and the ship sends one pulse every 100 m (a real echo sounder sends several pulses each second). The single pulse is slowed 20 times; on the voyage every pulse is slowed 3.5 times.
Not to scale: on the field the people and the wall are drawn larger than the 100 m distance; at sea each metre of depth is drawn about 1.7 times longer than a metre along the route.
Reduced motion shows the end of each clap, timing, pulse and voyage straight away, without the moving wavefronts.
Choose a piece of equipment to read what it does.
Not to scale · no sound played