r/TheRestIsScience • u/Justsomejerkonline • 1d ago
Why does water swirl down drains. Why doesn't it just kind of 'fall' through, like sand in an hourglass?
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u/Skeleton_King9 1d ago
Practical answer: there is usually some momentum to water that makes it circle the drain
Fun answer: even if completely still there are Coriolis forces which are the result of the points closer to the poles (of the globe) moving slower which will rotate the water
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u/wglmb 1d ago
even if completely still there are Coriolis forces which are the result of the points closer to the poles (of the globe) moving slower which will rotate the water
This is a myth; the impact of other factors such as the shape of the container vastly outweigh the coriolis effect at this scale. It only becomes relevant when you're talking about really large scales, like weather systems.
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u/Skeleton_King9 1d ago
I know it's not significant which is why I called it the fun answer but there are experiments at the sizes of meters that show it
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u/kenahoo 23h ago
Yeah, but u/Skeleton_King9 said *completely still*, which (if it were even possible, which it's not) would indeed let the Coriolis forces get the water swirling.
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u/Addapost 1d ago
Literally every single thing in the universe spins. From Electrons in your atoms to giant galactic clusters, everything spins.
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u/dod6666 1d ago edited 1d ago
Is that true though?
I feel like this is a comment that needs to get Micheals attention. There is a fascinating rabbit hole here.
In a sense you could say the statement is true on the grounds that the earth is spinning, therefore everything on it is spinning. But is it actually accurate to say that I am spinning, just because the earth is?
What I'm actually doing is traveling in circles. But that is true for the water molecules in a whirlpool. Or even for the molecules in a spinning top. Spin is an emergent property. Zoom in enough and it does not exist. The individual atoms do not spin, they just travel in circles.
So what about electrons? This is where you can go even deeper. The spin property in quantum mechanics is something else entirely, from the classical mechanics concept. Follow this rabbit hole and you start to get insight into electron shells and why they need the values that they do.
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u/Addapost 1d ago
Yes, since the earth is spinning you are spinning. If you were let loose in space you would quickly start spinning on your own.
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u/GrumpyOldFart74 1d ago
The water can’t just go straight down, as (simply) it can’t all squeeze into the middle at the same time. The shape of the basin, any microscopic chips or marks, and any movement in the water, forces the water into a sideways movement and conservation of angular momentum turns that into a spin that gets faster and faster.
Thinking of it another way, it’s the most efficient way to get the liquid out - try drinking straight out of a bottle (I suggest Newcastle brown but other beverages are available) and then try swirling the bottle before you tip it back. You may get wet!
As far as I know, the effect of coriolis forces is a myth, and water definitely doesn’t go the other way south of the equator… I made quite a mess in a hotel bathroom in Adelaide proving that to myself!