Shout in front of a cliff, and your own voice comes back. Bats find insects in the dark, and ships find the sea floor, with sounds that we cannot hear. In this course we study echoes, the way the ear works, the range of hearing, and the uses of ultrasound.
3 lessons, about 1 h 15 min3 simulations11 problems6 practice questionsPython in every lesson
Created by StemPy LabSound bounces off hard surfaces, like a ball off a wall. We hear an echo when the reflected sound returns at least 0.1 s after the original, so the wall must be at least 17 m away. Many reflections make a sound linger: reverberation.
The ear collects sound, the eardrum vibrates, three small bones make the vibration stronger, and the cochlea changes it to signals for the brain. People hear from about 20 Hz to 20 000 Hz; below is infrasound, above is ultrasound.
Ultrasound has a frequency above 20 000 Hz. It cleans small parts, finds cracks in metal and makes pictures inside the body, and SONAR uses its echoes to find the depth of the sea. Bats and dolphins hunt with it.
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