Hurricanes are large enough to be affected by the Coriolis force. Sinks draining water are not. Hurricanes spin counter-clockwise in the northern hemisphere. Water going down drains spins in random directions. Therefore, the cannon shell is deflected westward to the right , from the perspective of a person standing on the earth.
A gunner firing a cannon northward would find that the shell is also deflected toward the right. These sideways deflections are attributed to the Coriolis force, although there really is no force involved--it is just an effect of being in a rotating reference frame. The circulation directions result from interactions between moving masses of air and air masses moving with the rotating earth.
The effects of the rotation of the earth are, of course, much more pronounced when the circulation covers a larger area than would occur inside your bathtub. Even in a tub having a perfectly symmetric drain, the circulation direction will be primarily influenced by any residual currents in the bathtub left over from the time when it was filled.
It can take more than a day for such residual currents to subside completely. If all extraneous influences including air currents can be reduced below a certain level, one apparently can observe that drains do consistently drain in different directions in the two hemispheres. Finally, Thomas Humphrey, a senior scientist at the San Francisco Exploratorium, discusses in more detail the reasons why we do not see the Coriolis effect at work in the bathroom:. For a fee, they will allegedly demonstrate that the toilets flush in opposite directions.
It is only for show, however; there is no real effect. Yes, there is such a thing as the Coriolis effect, but it is not enough to dominate the flushing of a toilet--and the effect is weakest at the equator. Coriolis acceleration at mid-latitudes is about one ten-millionth the acceleration of gravity. Anyone claiming that this is some kind of myth has failed to notice that no one has said that they own a sink whih regularly goes down the "wrong" way.
I like the explanation for how the bucket on the equator trick works. I wouldn't have thought it would actually work by moving a few meters as the effect of the Earth's spin is at its weakest at the equator.
Simon, The northern hemisphere and southern hemisphere are both spinning in the same direction, the North and South are not spinning in opposite directions so water going down the plug whole is the same in either hemisphere.
Clash, Dunston, UK The earth is spinning counter-clockwise relative to the North Pole and clockwise relative to the South Pole, which causes the coriolis effect to be different on the Northern and Southern hemispheres. However, as a third year physics student I can assure you it has absolutely nothing to do with water spinning down the drain, even a very large drain.
It is, however, responsible for many weather effects such as hurricanes. Sam patera, Moorpark, U. I just "contradicted the laws of physics"! I filled the sink in my bathroom, pulled the plug, and observed the direction of rotation of the vortex. It was clockwise. I filled the sink again, pulled the plug, and immeidately gave the water a counterclockwise "swirl" with my hand. The swirling effect seemed to die out pretty quickly, but as water got to be very low in the sink a vortex formed, and it rotated counterclockwise.
Richard, USA No-one has mentioned numbers. For the Coriolis effect to make itself felt, the mobile medium air or water must travel thousands of Kms across the surface of the earth. A plug hole is a couple of cms across. Not enough distance for the rotation of the earth to have any discernable effect at all.
The water had been standing for about 15 minutes prior to me pulling the plug and was not obviously moving at all before I gently pulled the plug. I therefore must support the "random" argument. Paul Wright, Rochford UK Let's assume for the purpose of this argument that water goes one way in the north and appears to go the opposite way in the south.
IF this is true and I'm not saying it is, then it's not the water that changes direction but the angle of the viewer. In this argument the important factor is the relative position to the centre of the earth.
A simple demonstration is to put an object in you hand holding it at waist level and start turning it clockwise, keep turning it in the same direction and raise it above head height, now your looking from the other side and it is turning the otherway even though it never stopped turning in the same direction.
Or try to imagine a vortex of water going from your plug hole at the north pole straight throught the centre of the earth to another plug hole at the south pole, the vortex only goes one way but the water seems to be going in different directions in the two holes as viewed by the observer.
Ergo the water only ever goes one way north or south of the equator, it's the viewer who changes position relative to the vortex. Well, here is my theory - You saw it here first! Electrons have two properties, spin and charge. Spin has recently been discovered and is implemented in the read head of computer hard drives.
Spin makes it possible for plastic materials to be magnetised and conduct electricity. Since everything has electrons including water , and electrons are affected by magnetic fields Example - the earths magnetic field , it is my belief that spin holds the answer to the fundamentals of how gravity works and the answer to this age old question of direction of water spinning down a plughole could be answered.
As for the Coriolis Effect, this describes the conservation of momentum and explains why the water direction speeds up as the amount decreases. As for the basin shape, the tap last used, the way the plug was taken out - these all will factor in and any of these could dominate if allowed to.
I propose a test for you crazy people out there. This will prove if magnetisation is responsible for the direction! Coil the wire around the bucket at least times. Connect the wire to a battery so current flows one way through. Wait 1 hour for the water to settle then drain the bucket.
Refill the bucket, reverse the current direction and repeat the experiment. You will need to test both directions at least 5 times for a set of results worth considering.
Nick Hardman, Bury England Why are people still debating this issue? If you are still stupid enough to question this run one tap into a basin and then pull the plug then do the same with the other plug Guess what happens Thank you to all those people with enough grey matter to help clarify this. All those people who have 'seen' the so-called demonstrations at the equator probably also believe the magician really does saw the lady in half Mark , Reading UK As a physics teacher of 43 years experience, who was present only last week on the Equator in Kenya, I am amazed at how many people were deceived by the trickery of the Coriolis effect 'demonstrators'.
The man we watched clearly made the water spin in his required direction by holding the dish in his hand and pouring in the water in one direction or the other. When on the Equator line he tilted the dish whilst filling it, to avoid much spinning, then put the matchstick down the side so that it was held in place by the meniscus and not dropped into the centre of the bowl.
Even then, the match 'tried' to move with the slightly spinning water. If you try this at home you can succeed after 5 minutes of practice. There's no need to spoil a dish by drilling a hole in the centre. The trickster put the hole in his dish merely to make it more convincing. Alan Shepherd, Huddersfield UK The rotation of the earth producing Coriolis forces that make the vortex flow anti-clockwise in the northern hemisphere and clockwise in the Southern hemisphere is a myth.
A quick calculation of the magnitude of the Coriolis effect on the mass and time scale of the draining of a sink are WAY too small to account for vortex formation. The fact that a given sink may always flow in the same direction is most likely due to some asymmetry in the geometry of the sink and the drain. Wayne Gill, Willenhall, UK Instead of people blindly asserting that this is true, why not carry out experiments at home? Fill your basin, and leave it to settle for 15 mins.
Gently pull the plug and observe the direction. If the effect is real, you would expect 8 or 9 out of 10 to flow the "correct" direction. Ben, London UK A vortex will form in either direction, depending on the underlying currents in the body of the liquid. Re the 'convincing' demonstrations in Kenya showing the change of direction on crossing the painted line in the road: the 'equator', if the writer s had carried on further up the road he or she would have seen the same 'proof' being irrefutably demonstrated for a small fee across another painted equator line.
Oh, and again, further along the road some more! Obviously convincingly performed, but simply a sleight of hand. Good on them!! Andy , Black Isle UK The reason water rotates down the plug hole is actually due to both reasons previously stated.
However, this would mean, should the water in its container be completely still and the container itself symmetrical, then the water would not rotate at all. In short, water is controlled by a force however, definitely not the Coriolis force, as its effect is far to small to be appreciated in this scenario , but the only reason we ever see water rotate one way down the plug hole in our baths, is simply due to baths shape. My upstairs bathroom clearly sits in a different hemisphere than my downstairs clockroom as they spin in different directions to each other!
I know I'm in South Bucks, but it feels just too cold to be on the Equator. They have identical sinks and central mixer tap - i filled the sink and left for 10 minutes before releasing the plug lever on the tap, so no hands in the water! Did this 3 times and each time they span in opposite directions to each other but always the same as they had previously.
The reason the water spins different ways on different sides is related to the moon and the earth, the sun and the other planets!!! Thank you for all of the answers. I'm still no further forward though but the physics teacher with 43 years experience sounds convincing.
David, Oxford Don't know if this is an age-old thread or what. Anyway, I see that the answers are confusing, to say the least. I admit I also thought the water would spin one direction in the northern hemisphere and another in the southern that is - relative to the viewer, which of course views the spinning from opposite directions. I also thought the coriolis effect was what caused it. I searched for this only to find out what happened near equator. People post their opposite assertions, some claim to have tested it with opposite results and no one posts any sources for their claims.
Word against word. The Wikipedia, however, must cite sources and can be corrected by knowledgeable scientists. The Wikipedia asserts that the coriolis forces does have an effect, and would cause the water to spin counter-clockwise in the northern hemisphere, and clockwise in the southern.
It might also help to have something floating in the water to make the motion more visible. For instance, sprinkle some pepper on the water right after stirring to see its motion more easily. The students can stir the water with a large spoon, a stick, or, after rolling up sleeves, just with a hand see Figure 2. Now wait a few minutes until the water is hardly moving and then open the drain.
Students will then notice how the water ends up swirling down the drain in the same direction that they stirred it earlier. Repeat the experiment stirring counterclockwise. Students should conclude that the water swirls down the drain in the same direction that it was initially moving. Do you have extra time to fill? Ha ha. If so, repeat the investigation waiting longer after stirring for the water to settle.
Thus even the slightest, imperceptible movement will get amplified into fast swirling. The reason this happens is the same as why a spinning ice skater will spin faster as she pulls in her arms and legs see Figure 3. It has to do with a quantity known as angular momentum.
The angular momentum is the product of three quantities: the mass of the object, the size of the object, and the spinning speed. For an object moving around in a circle, like a ball on a string being twirled around, the size in this case would refer to the distance of the ball from the center of the circle, i. Keep that in mind when we get back to the swirling water. One last bit of terminology: When something stays the same, scientists say it is conserved.
So the idea that the angular momentum stays the same is known as the conservation of angular momentum. Ask students: When the spinning ice skater starts to pull in her arms and leg, which of those change and which stay the same?
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