Flushing question

[CoffeeGuy]

In north America, when a toilet is flushed, the water swirls in a vortex, counter clockwise. I have heard, in Australia, the vortex is clockwise. Is this true ? And if so, why ?

[freak_in_cage_10k]

yeah, its true, its because of the hemisphere, earths gravity etc.

dont really understand the technical stuff behind it

[canadateck]

I heard it was because of the way the toilets are made? Does it happen in the bath also?

[BJ_M]

not the way they are made is the cause - except they are made to work with the way the water goes naturally ..

bathtub also do the same thing ..

[Supreme2k]

It's the coriolis effect, yo.

[rallynavvie]

It's the coriolis effect, yo.

Indeed that. If you're ever travelling near the equator you've gotta try this, Get a couple large buckets and a big funnel. Put some stuff in the water to float around to help show which way the water rotates and try on either side and as close to the equator as possible, it's kinda neat to see.

[Guest]

didnt work for me in Chile. Counter clock wise.

[Supreme2k]

That's because, to make you feel better, they had American toilets installed. Plus, your stool size may have exerted their own gravitational pull, thus cancelling out the effect.

[Guest]

peed,....... happened when I drained the sink as well.I was quite disappointed. My first and only trip to the S. Hemisphere,ruined!

[pfh]

didnt work for me in Chile. Counter clock wise.

Same for my observations in Peru. I say it's bull! Depends on the toilet.

[BJ_M]

Question: Does my bathtub drain differently depending on whether I live in the northern or southern hemisphere?

Answer: No. There is a real effect, but it is far too small to be relevant when you pull the plug in your bathtub.

Because the earth rotates, a fluid that flows along the earth's surface feels a "Coriolis" acceleration perpendicular to its velocity. In the northern hemisphere, Coriolis acceleration makes low pressure storm systems spin counterclockwise; however, in the southern hemisphere, they spin clockwise because the direction of the Coriolis acceleration is reversed. This large-scale meteorological effect leads to the speculation that the small-scale bathtub vortex that you see when you pull the plug from the drain spins one way in the northern hemisphere and the other way in the southern hemisphere.

But this effect is VERY weak for bathtub-scale fluid motions. The order of magnitude of the Coriolis acceleration can be estimated from size of the "Rossby number" (1) (see below). The effect of the Coriolis acceleration on your bathtub vortex is SMALL. To detect its effect on your bathtub, you would have to get out and wait until the motion in the water is far less than one rotation per day. This would require removing thermal currents, vibration, and any other sources of noise. Under such conditions, never occurring in the typical home, you WOULD see an effect. To see what trouble it takes to actually see the effect, see the reference below. Experiments have been done in both the northern and southern hemispheres to verify that under carefully controlled conditions, bathtubs drain in opposite directions due to the Coriolis acceleration from the Earth's rotation (2).

Coriolis accelerations are significant when the Rossby number is SMALL. So, suppose we assume a Rossby number of 0.1 and a bathtub-vortex length scale of 0.1 meter. The Rossby number is defined as

Rossby number = U/(2*L*w)

where U is the velocity of a fluid element, L is the scale of the fluid motion, and w is the earth's rotational velocity ( = 1 rotation/day). In conventional units, the earth's rotation rate is about 10-4/second, so solving the above equation for the fluid velocity, we get that Coriolis acceleration in your bathtub is significant for fluid velocities of less than 2 x 10-6 meters/second. This is a very small fluid velocity. How small is it?

Well, we can take the analysis a step further and calculate another, more famous dimensionless parameter, the Reynolds number.

The Reynolds number is = L*U*density/viscosity

Assuming that physicists bathe in hot water the viscosity will be about 0.005 poise and the density will be about 1.0, so the Reynolds Number is about 0.04.

Now, life at low Reynolds numbers is different from life at high Reynolds numbers. In particular, at low Reynolds numbers, fluid physics is dominated by friction and diffusion, rather than by inertia. That is, at low Reynolds numbers the time it would take for a small piece of fluid to move a significant distance due to an acceleration, is greater than the time it takes for that piece to break up due to diffusion.

Ideas about which way a bathtub will drain have also been cited for giving the direction water circulates when you flush a toilet. This is surely nonsense. In this case, the water rotates in the direction in which the pipe points, that carries the water from the tank to the bowl.

[rallynavvie]

The effect is stronger near the equator IIRC.

[stiltman]

So if you're at 0 longitude and 0 latitude, it wont spiral. It will just go striaght down?

[rhegedus]

Strangely, this very issue was addressed by Michael Palin in the travel documantary, 'Pole to Pole', by filling a bucket with a hole at the botton with water and watchng the way a floating object rotated on its surface.

water.wmv

We should get Pac on the case as a Southern hemisphere representative........ saying that, Australia is backwards so it won't prove a thing :P

[SquirrelDip]

This is a myth - it has nothing to do with the coriolis...

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

The direction of rotation of a draining sink is determined by the way it was filled, or by vortices introduced while washing. The magnitude of these rotations may be small, but they are nevertheless gargantuan by comparison to the rotation of the Earth.

[rhegedus]

The direction of rotation of a draining sink is determined by the way it was filled, or by vortices introduced while washing. The magnitude of these rotations may be small, but they are nevertheless gargantuan by comparison to the rotation of the Earth.

That doesn't apply to still fluids........

[SquirrelDip]

The point they're making is that there is always a certain amount of residual motion within the liquid and no matter how small that residual motion it is still "gargantuan" compared to the rotation of the earth.

[BJ_M]

yes -- what i wrote here explains it in detail ..

https://www.videohelp.com/forum/viewtopic.php?p=1305978#1305978

[stiltman]

yes -- what i wrote here explains it in detail ..

https://www.videohelp.com/forum/viewtopic.php?p=1305978#1305978

You wrote all that? or did you copy and paste all that?

[rhegedus]

The point they're making is that there is always a certain amount of residual motion within the liquid and no matter how small that residual motion it is still "gargantuan" compared to the rotation of the earth.

Surely one would exoect this residual motion to be random and thus the vortex created would be clockwise/counter-clockwise on an equal number of occasions.

[SquirrelDip]

The point they're making is that there is always a certain amount of residual motion within the liquid and no matter how small that residual motion it is still "gargantuan" compared to the rotation of the earth.

Surely one would exoect this residual motion to be random and thus the vortex created would be clockwise/counter-clockwise on an equal number of occasions.

I don't know about that... Ever time you open the tap on your sink or flush the toilet the water will probably flow the same each time.

Try this... Fill a sink to the top, stir it clockwise and once the stirring is smooth pull the plug. Then do the same thing counterclockwise. If the coriolis is significant it should force the flow to redirect in one of the cases.

(I just did this and flow direction never changed...)

[rallynavvie]

It isn't strong enough to reverse the flow if it is already started in one direction. We would probably notice the energy required to cause that to happen. The idea is it would happen from a standstill more often over several attempts in one direction than another.

[rhegedus]

What do those of you who think the effect is negligible think of the video clip I posted?