hi,

 

i've heard that water drains down a plug the opposite way in australlia than it does in the uk, but what happens if you go to the center of the earth.. withh the water just fall directly down?

i've heard that water drains down a plug the opposite way in australlia than it does in the uk, but what happens if you go to the center of the earth.. withh the water just fall directly down?

 

What you heard was wrong. The Coriolis force is so small on the scale of a sink or basin that it cannot be responsible for forming any vortex. The reason water goes clockwise or anti-clockwise is due to the shape of the basin and any residual motion of the water; for containers with forced water, the rotation will be in the direction that the water is forced.

I once heard that tornadoes and cyclones are also affected by Coriolis force, causing them to rotate clockwise or anticlockwise. I suspect it's just an extrapolation from the plughole mistake. In reality, apparently pressure determines the direction of cyclones.

I would be willing to stake my reputation on the fact that weather systems are directed by the Coriolis force. You may feel that's not much of a stake to bet, but its all I've got.

Wow. This is something this wide-eyed ignoramous has always wondered about. So what is the Coriolus force?

What you heard was wrong. The Coriolis force is so small on the scale of a sink or basin that it cannot be responsible for forming any vortex. The reason water goes clockwise or anti-clockwise is due to the shape of the basin and any residual motion of the water; for containers with forced water, the rotation will be in the direction that the water is forced.

Can you cite experimental evidence?

Er, your toilet?

 

Seriously, here's quite a good pratical page: -

http://www.ems.psu.edu/~fraser/Bad/BadCoriolis.html

I would be willing to stake my reputation on the fact that weather systems are directed by the Coriolis force. You may feel that's not much of a stake to bet, but its all I've got.[img']http://www.scienceforums.net/forums/images/icons/icon7.gif[/img]

Beaten by my own smugness again. Dammint, when will I learn to research?

I would be willing to stake my reputation on the fact that weather systems are directed by the Coriolis force. You may feel that's not much of a stake to bet, but its all I've got.[img']http://www.scienceforums.net/forums/images/icons/icon7.gif[/img]

 

 

And you would win that bet.....

What you heard was wrong. The Coriolis force is so small on the scale of a sink or basin that it cannot be responsible for forming any vortex. The reason water goes clockwise or anti-clockwise is due to the shape of the basin and any residual motion of the water; for containers with forced water, the rotation will be in the direction that the water is forced.

 

Won't it rotate counter-clockwise in the northern hemisphere all other things being equal? I live at 45 degrees latitude. I think the force is stronger here than, say, 5 degrees latitude. But is it also stronger here than at the North Pole?

 

My "completely still" 2 foot diameter basin of water would have more "potential" (insert correct terminology here for the differences in the velocity squareds) across my north/south 2 feet (relative to a polar axis rest frame) than in the other 2 cases.

Won't it rotate counter-clockwise in the northern hemisphere all other things being equal? I live at 45 degrees latitude. I think the force is stronger here than' date=' say, 5 degrees latitude. But is it also stronger here than at the North Pole?

 

My "completely still" 2 foot diameter basin of water would have more "potential" (insert correct terminology here for the differences in the velocity squareds) across my north/south 2 feet (relative to a polar axis rest frame) than in the other 2 cases.[/quote']

All other things being equal, yes there will be a small effect:

 

 

Here's a plausibility/ order of magnitude argument. Angular momentum is conserved, meaning that mv*r is a constant. An object moving at a certain speed will move twice as fast if you shorten the radius by a factor of two. So as water drains, it picks up speed in moving closer to the hole.

 

Now, the earth rotates once per day, and that's the source of the motion we are investigating. Your 1 meter diameter basin (i.e. fairly big) is a shade over 3 meters in diameter, so a molecule of water is moving ~3m/day at the north or south pole (multiply by sin(latitude) to adjust for your location) or 35 microns per second. You cut a 1 cm hole (smaller than most drains) in the basin to drain the water, and look at the speed of the water at the edge. 3.5 mm/sec, because you have reduced r by a factor of 100, or close to 3 seconds to complete a revolution - and this is the fastest it gets. Water that started closer moves slower.

 

This is a lot slower than the effects I see, even favorably exaggerating all dimensions by a fair amount. So something is happening, but it's a small effect.