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Often in sinks, toilets, bathtubs, etc., the water is already moving, though
maybe very slowly. As the water drains, that slow rotation becomes more
visible. In the case of a sink or bathtub, where the width of the pool
decreases as it drains, the rotation increases speed as it drains. This is
because angular momentum is conserved (think of a figure skater speeding up
as she pulls her arms into her body -- it is the same effect). In a draining
tank, the water by the drain has the least momentum. As it leaves, the
remaining water with more momentum takes its place. If an object with
angular momentum moves closer to the center of its rotation, it speeds up.
So, the water gradually picks up speed, and you see rotation.
Even if there is *no* angular momentum to start with, fluid can start to
rotate. This is called a "secondary flow". To understand why secondary flows
develop, you have to understand the nature of viscosity. When molecules of a
liquid are attracted to each other, they resist being pulled apart. For
example, when you move your hand through water, you are dragging molecules
of water with your hand. Some of the resistance is simply the inertia of the
water, but much of it is viscosity. The molecules that you accelerate pull
on the ones next to them, and those next to them, etc. Moving water
molecules across each other, a 'sideways' force, is called 'shear'.
Resistance to shear is called viscosity.
Imagine a large cylindrical vessel full of water with a small drain at the
bottom. When you open the drain, water starts to flow down the hole. Of
course you have taken great care to ensure the water is completely
stationary first, and that opening the drain does not perturb it. As the
water flows downward, it drags the molecules around it due to viscosity. At
the point of the drain, some of the molecules go down the drain, but other
ones cannot fit. Yet, they have still gained some energy by being dragged by
the ones that did go down the drain. They have to go somewhere, and since
they cannot go down, and gravity makes it hard to go up, they go sideways.
Over time, they start a rotational flow, called 'secondary flow'. Over a
short period of time, viscosity, caused by the molecules' mutual attraction
to each other, ensures that they move together in the same direction. In
time, a vessel with a drain full of stationary water will develop a quite
noticeable rotation due to secondary flow.
Another place where secondary flows commonly occur is in tea. Here, the
opposite occurs: a rotational flow causes vertical motion. If you drink
green tea, watch the leaves as you stir it. Even though you are stirring the
tea in a rotational direction, you can see the leaves are pushed upward. The
upward motion, caused by viscosity in response to the rotation, is another
example of secondary flow. Of course, depending on how you stir, it could be
your spoon moving them up, not secondary flow. So be careful. :)
A lot of research has been performed to understand how and when secondary
flows occur. It turns out that any viscosity gradient can cause a secondary
flow. Sometimes secondary flows are hard to see (they can be very
small/slow), but they are there! This is the underlying reason for the
'swirl' you see.
If you travel from the northern hemisphere to the southern, you will notice that water 'swirls' counterclockwise. Simply enough, it is because of the rotation of the earth acting on the water in conjunction with gravity.
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Why does water run down the bathtub drain like a swirl?
Water runs down the bathtub drain in a swirl due to the Coriolis effect, caused by the Earth's rotation. The direction of the swirl is determined by the hemisphere you are in—counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. However, for small-scale drains like in a bathtub, factors like the design of the drain and how the water enters play a more significant role in determining the direction of the swirl.
How do i unclog a bathtub that has dried paint stuck down in it to let the water drain?
via push it
What part of speech is the word Bathtub in the sentence Did my smelly soap slip down the bathtub drain?
In this usage, "bathtub" is an adjective, modifying the noun "drain."
Orbeez down the drain?
Well if you have another bathtub then use it because if the pipe has no water in it the orbeez will dry out and go into the sewer easily without blocking the drain
When you flush the toilet fills with water to the top then gushes down but water comes up in the sink and bathtub what causes this?
The sewer line is plugged or collasped. The sink and bathtub may drain because they drain at a slower rate. Toilet is all at once and the drain can't handle it. Water has to go somewhere so it backs up in the sink and tub.
My son put a plastic shampoo cap down the bathtub drain It was working fine but now no water will go down at all I know that chemicals and hot water won't break down the plastic what will work?
Calling a licensed plumber to remove it
How many Ethiopians can you fit in a bathtub?
This is a joke and it is answered as; None, since they keep slipping down the drain.
Will running the hot water kill a spider in the bathtub?
Running hot water in the bathtub is unlikely to kill a spider as they can usually survive in water for a period of time. It would be more effective to try to remove the spider using a cup or a piece of paper and release it outside.
How does a bathtub overflow work?
A quick way would be to drop into a plumbing supply store. They often have tubs on display with the overflow drain hooked up. You will be able to see where the overflow water goes down the drain. Des Perado
When water drains out of the shower bathtub why do you hear a really loud ping ping ping noise in the wall across from the shower bathtub as it goes down the drain fast at first slower as it empties?
You are probably hearing the hot water hitting the cold pipe which causes expansion thus the pinging sound. Drain speed could probably be clogged vent stacks try cleaning them out.
How do you thaw a bathtub drain?
Pour hot salt water down it, or alcohol if that fails. You can also just try putting a space heater next to it to thaw it externally if you can get access to the pipe.
Bathtubs and sinks have for the water to go down?
The water goes down the plughole/drain and then down the pipes.
