I remember when I was young I saw people emptying the water from their

[equilibrum]

I remember when I was young I saw people emptying the water from their tanks using a flexible tube(without any pumps or other mechanical device). If I am not wrong, you first fill the tube with a little bit of water and make a U shape,then you close the 2 ends with your thumbs and put the tube in the tank and somehow it begins to suck the water out of the tank.

I'm curious to know what causes this? I thought of Bernoulli's principle/effect but I don't really understand the explanation on Wikipedia. Never learned anything about it in school either.

Can anyone explain this to me? In simple terms and/or with simple formulas please. Just wanted to know :D

 

[Vanadium 50]

If you Google "siphon", I think you will get everything you need to know.

 

[equilibrum]

If you Google "siphon", I think you will get everything you need to know.

That explained a lot ^^ still a little confused about hydrostatic pressure though.

 

[vlado_skopsko]

First you need to fill the tube to the highest point and then the water will flow if the end of the tube is lower from the surface of the fluid in the tank. And and the speed of the water flowing out will depend of the potential (height) difference(H) between the surface of the water of the tank (first section) and the opening of the tube (that will be our second section).

If we suppose that the thank and open end of the tube are open to the a atmospheric pressure and speed of the surface of the fluid in the tank is near zero then the Bernoulli equation will become:
$$\rho$$v²/2g=H
from that
v=$$\sqrt{}2gH$$
If the height deference (H) is 0 then then the speed will be 0, so no water will flow.

 

[equilibrum]

First you need to fill the tube to the highest point and then the water will flow if the end of the tube is lower from the surface of the fluid in the tank. And and the speed of the water flowing out will depend of the potential (height) difference(H) between the surface of the water of the tank (first section) and the opening of the tube (that will be our second section).

If we suppose that the thank and open end of the tube are open to the a atmospheric pressure and speed of the surface of the fluid in the tank is near zero then the Bernoulli equation will become:
$$\rho$$v²/2g=H
from that
v=$$\sqrt{}2gH$$
If the height deference (H) is 0 then then the speed will be 0, so no water will flow.

thanks for the two equations! i am playing around with them. Just to check, v = velocity of fluid , g = 9.81m/s^2 and p = fluid density?

 

[vlado_skopsko]

Yes. At first how the siphon works is a little bit counterintuitive.

 

[equilibrum]

Yes. At first how the siphon works is a little bit counterintuitive.

Yeah cause it seems to go against gravity. It's fine though :)