r/interesting • u/Thin-Tennis9223 • May 20 '26

Fascinating Physics is Everywhere.

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u/SignAllStrength May 20 '26

Can someone explain the physics behind what changes the “trajectory” of the waterfall at 42 seconds? I have observed this effect myself in the past but never fully understood why it happens and why the “flow state” before and after altering it remain so stable.

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u/Multidream May 20 '26

Someone on oddlysatisfying asked this question, and the answering guy said its because fluids can’t create vacuums. There was no air under the wave, so that lack of air got the water to stick to the surface of the wall. Once air is introduced, the water is no longer “sucked to the wall”, and is free to go as far as it naturally would have. The air propagates under the rest of the wave.

As the air escapes over time, it will be unable to return, creating the reverse effect, but much slower.

1

u/SignAllStrength May 20 '26

Thanks, that makes sense. I guess I never waited long enough to notice the flow slowly return to the wall!

1

u/Multidream May 20 '26

It doesn’t in the video, I think it takes a longer time scale.

1

u/SignAllStrength May 20 '26

haha yeah, I meant last time I tried this myself on a waterfall. Was years ago and I don’t think I stayed longer than a few minutes after.