When waves pass around small (we’re talking small compared to the wavelength of the wave) objects, they diffract. People in the audience of a concert can hear really well if they are sitting right behind a pillar because the sound waves are large enough to bend around it (which is actually because of both diffraction and reflection effects). Diffraction helps sound bend around obstacles. You can sometimes hear conversations around corners because of diffraction.
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Waves also diffract if they spread out after moving through small (again, smaller than wavelength-size) openings, like light going through a slit cut with a razor.

The amount a wave diffracts (bends) depends on the wavelength. Lower frequencies bend around objects better than higher frequencies. If you’ve ever watched a lightning and thunder storm, you know that there’s a lot more sound (like a sharp crack) when the lightning is closer  (you hear both higher and lower frequencies) than when it’s more distant (mostly lower frequencies). Owls use low frequency sounds to transmit sounds further than the higher frequency bird twitters.

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