Naked Science Forum

On the Lighter Side => That CAN'T be true! => Topic started by: Make it Lady on 08/04/2008 16:45:53

Title: Which scientific myth have you been suckered by?
Post by: Make it Lady on 08/04/2008 16:45:53

I believed the water down the plug hole myth for sooooo long!

Title: Which scientific myth have you been suckered by?
Post by: JimBob on 08/04/2008 17:48:49

QM

Title: Which scientific myth have you been suckered by?
Post by: DoctorBeaver on 08/04/2008 20:04:16

I believed that we only use 10% of our brain until just a few years ago.

Title: Which scientific myth have you been suckered by?
Post by: Make it Lady on 08/04/2008 21:21:29

I think I still do...use that much, I mean.

What led you to the explosion of this myth?

I was researching the science behind one of the hands-on exhibits at INTECH 'The Vortex.' I discovered that in loads of books it said that the water spins down the plug hole in different directions depending on which hemisphere you were in. It was even written up on the explanation board by the exhibit. My boss had written it. When I discovered it was untrue I had to tell my boss she was wrong. She was a bit scary so I chickened out for a while. It is probably still wrong to this day. I feel guilty now and should go back and tell them. 

Title: Which scientific myth have you been suckered by?
Post by: DoctorBeaver on 08/04/2008 21:40:51

The myth was exploded in my eyes when I saw EEG traces.

Title: Which scientific myth have you been suckered by?
Post by: Madidus_Scientia on 09/04/2008 11:03:26

Quote from: Make it  Lady on 08/04/2008 16:45:53

I believed the water down the plug hole myth for sooooo long!

It is true, but only of very controlled experiments. you can't just fill your sink up then unplug it and watch it, its called the coriolis effect and is only a very insignificant force in terms of deciding the direction of the water spiralling, any motion in the fluid before you pulled the plug would mostly determine it. To actually observe the effect you need a very large shallow dish of uniform shape, leave it for a long time so that any of the initial motion in the fluid has pretty much all stopped, and would have to be at constant temperature to stop any convection currents occuring, and then let it drain through a very small hole (you'd have to unplug from the bottom, putting your hand in the fluid and pulling a plug out would obviously give the fluid motion again).

Then the effect can be observed, it would spiral counterclockwise in the northern hemisphere, clockwise in the southern.

Title: Which scientific myth have you been suckered by?
Post by: Make it Lady on 09/04/2008 18:58:43

Quote from: Madidus_Scientia on 09/04/2008 11:03:26

Quote from: Make it  Lady on 08/04/2008 16:45:53

I believed the water down the plug hole myth for sooooo long!

It is true, but only of very controlled experiments. you can't just fill your sink up then unplug it and watch it, its called the coriolis effect and is only a very insignificant force in terms of deciding the direction of the water spiralling, any motion in the fluid before you pulled the plug would mostly determine it. To actually observe the effect you need a very large shallow dish of uniform shape, leave it for a long time so that any of the initial motion in the fluid has pretty much all stopped, and would have to be at constant temperature to stop any convection currents occuring, and then let it drain through a very small hole (you'd have to unplug from the bottom, putting your hand in the fluid and pulling a plug out would obviously give the fluid motion again).

Then the effect can be observed, it would spiral counterclockwise in the northern hemisphere, clockwise in the southern.

Read this and weep

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

I think you will find the forces are too weak to effect your plumbing...sorry.

Title: Which scientific myth have you been suckered by?
Post by: Bored chemist on 09/04/2008 21:00:38

It seems the equator must run through my parent's bathroom (in the North of England).
The sink drains one way and the bth swirls the other.

Title: Which scientific myth have you been suckered by?
Post by: Make it Lady on 09/04/2008 22:31:31

If you go to villages roughly around the equator they have special vortex shows that demonstrate the myth. Unfortunately not all of the villages are actually on the equator but it is obviously a good trick for the tourists.

Title: Which scientific myth have you been suckered by?
Post by: Madidus_Scientia on 09/04/2008 23:57:36

Quote

Read this and weep

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

I think you will find the forces are too weak to effect your plumbing...sorry.

i know that, but in controlled experiments it does work. this is from the page you posted, which is pretty similar to what i said before:

Is it possible to detect the Earth’s rotation in a draining sink?

    Yes, but it is very difficult. Because the Coriolis force is so small, one must go to extraordinary lengths to detect it. But, it has been done. You cannot use an ordinary sink for it lacks the requisite circular symmetry: its oval shape and off-center drain render any results suspect. Those who have succeeded used a smooth pan of about one meter in diameter with a very small hole in the center. A stopper (which could be removed from below so as to not introduce any spurious motion) blocked the hole while the pan was being filled with water. The water was then allowed to sit undisturbed for perhaps a week to let all of the motion die out which was introduced during filling. Then, the stopper was removed (from below). Because the hole was very small, the pan drained slowly indeed. This was necessary, because it takes hours before the tiny Coriolis force could develop sufficient deviation in the draining water for it to produce a circular flow. With these procedures, it was found that the rotation was always cyclonic.