Why does water exiting a basin rotate one way in Northern hemisphere and the opposite way in Southern Hemisphe

Answer 1

I think this is an urban myth

Answer 2

As many answerers have already said this is something of an urban myth. Try for yourself - you can get the water to go down either clockwise or anticlockwise if you give it a start, whichever hemisphere you are in (or indeed at the equator). Now if there were no eddies in the water and no irregularities on the surface of the bath or plughole then the 'Coriolis effect' could theoretically act upon the water and cause it to spin in different direction in either hemisphere but a) this situation would never occur in the real world and b) it would take so long to have an effect that the water would all have drained away first unless you had a very very very large bath!

The 'Coriolis effect' does however have a noticeable action on atmospheric and oceanic circulation (although again there are other factors also at play) and you will find that atmospheric 'highs' and lows' spin in opposite directions either side of the equator. This is because they stretch over an appreciable fraction of the Earth's circumference and so one side of the cyclone or anticyclone is appreciably closer to the Earth's axis of spin than the other. The rotation of the Earth has the effect of displacing moving objects to the right in the N hemisphere and to the left in the S hemisphere.

Answer 3

It's because of the rotation of the earth. The spin is in the same direction at all times. However, because the earth is a sphere, one half of it is on top and one half is on the bottom. For each hemisphere, the direction of spin is opposite. It's not as noticeable at or near the equator, because there the spin is pretty much the same (also, there is a greater tangential force there), but as you go towards the North and South Pole, the spin changes to the completely opposite direction.
This can be demonstrated by spinning a ball. If a point on the top of the ball is spinning clockwise, then a corresponding point on the bottom is spinning counterclockwise, and vice versa.

Obviously alot of the answerers have never left home.

Answer 4

Whilst the Coriolis effect has a small part to play in water flowing in different spiral directions in opposite hemispheres, the major factor in the direction of flow is the geometrical design of the bath, basin or toilet bowl.

Answer 5

The coriolis effect is due to the reduction in rotational speed as you move away from the equator; a particle moving north or south is going faster relative to the ground beneath it and is apparently deflected. However the difference in rotation speed from one side of your sink to the other is absolutely tiny. Other disturbances in the water would vastly outweigh any effects.

If coriolis forces mattered over such a tiny distance, you wouldn't be able to walk northward or southward without veering off course!

Answer 6

True

The scientist Magnus Pyke wrote a book called 'Butter Side Up' in which he described this effect, which is generated by Coriolis Force.

The experiments were carried out in very controlled circumstances, so looking at your bat water going down the plughole is only a vague approximation, but true, nevertheless.

Answer 7

The reason why water (usually) rotates one way in the north and one way in the south is not due to the force in the Earth (I don't recall what it's called) but because of the brands of sink, baths, etc.
The brands used in the north usually come from different manufacturers than the types supplied in the southern hemisphere.
The force in the earth (I believe caused by it's rotation) is too weak to affect the draining of water to rotate in specific ways.

Answer 8

If you imagine two places, exactly opposite each other on the earth, one in the north, one in the south, viewed from one location only, they both rotate in the same direction. At the other location, you are just looking at the other side of it.

Answer 9

It doesn't.

"The water in the sink/basin is not stagnant -- that is it has eddy currents either clockwise or counter clockwise depending upon irregularities in the sink, the location of the faucet with respect to the drain, temperature gradients,...and a list of other origins. ... Once the water with a small angular component enters the mouth of the drain, the velocity gradient in the down pipe accelerates the angular motion and a vortex forms."

Answer 10

This is called the Coriolis Affect, and is caused by the rotation of the earth.

Answer 11

because our earth rotates around its axes in the same direction