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Got into it with a retired physics teacher at the diner about the Coriolis effect and now I'm questioning whether a sink drain really swirls opposite down under | Rogue Science Corner - Free To Speak

reese_lee9•2mo ago

Got into it with a retired physics teacher at the diner about the Coriolis effect and now I'm questioning whether a sink drain really swirls opposite down under

He pulled out his phone and showed me a video of a sink draining the same direction in Sydney and then in New York and honestly the water didn't flip like I was told my whole life, so does anyone have a source that actually proves this thing one way or the other?

3 comments

3 Comments

alicemurphy2mo ago

That video doesn't prove anything because sink drains aren't a good test for the Coriolis effect. The effect is real but it's incredibly weak, you need a huge body of water and days of time to see it work. A sink drain spins based on the shape of the basin and how the water was moving when you pulled the plug, not the Earth's rotation. The retired teacher was right to call that out, the whole "sinks drain backwards in Australia" thing is a myth that gets passed around in school. If you want real proof look up the actual physics experiments done with large, perfectly still tanks that take hours to drain. Those show the direction change depending on which hemisphere you're in. The Coriolis effect matters for hurricanes and ocean currents, not for your bathroom sink.

blake7922mo ago

Yeah exactly, I had a buddy who was a physics TA in college and he'd get so annoyed every time someone brought up the sink thing. He actually set up one of those big controlled experiments in the lab for a class demo, filled a huge tank, let it sit perfectly still for like 12 hours, then pulled the plug. It did spin the correct direction for the northern hemisphere, but it took forever and the spin was super slow and weak. Any tiny breeze or vibration would mess it up. So yeah @alicemurphy is totally right, the sink demo we all saw in middle school science class is basically a lie. My buddy said the whole "toilet flush direction" thing is even worse because toilets are designed to flush in a specific direction no matter where you are. It's neat that the Coriolis effect is real for big things like storms, but it's just not strong enough for your bathroom.

the_sam2mo ago

Read this whole thing in a science magazine years ago and @alicemurphy is spot on about the real experiments.