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Disclaimer: I'm not a physicist.

If you take an apple or a ball (or a cylinder works too) and put it under a tap such that the water falls down the side (not the centre) of the sphere, you get water flow roughly like this:

Water flow over an apple

It seems to me that the fluid is sticking to the surface of the ball and due to viscosity or whatnot the water holds itself together and creates this strange “following the direction of the ball” behaviour until the angle of the surface would be upward and then gravity is greater than the momentum + this stickiness and it falls down.

What do you call this kind of phenomenon? Does this specific case have a name? Has it ever been used for something practical? I expect the speed that the water's falling also contributes, e.g. at terminal velocity it might just brush right past the apple rather than being curved. Is that right?

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  • $\begingroup$ London Dispersion Forces, or Van der Waal's Forces $\endgroup$ – Kenshin Sep 16 '13 at 11:34
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    $\begingroup$ Related, if not the same, as this thread. You may find it interesting. $\endgroup$ – Eduardo Guerras Valera Sep 16 '13 at 14:25
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What do you call this kind of phenomenon? Does this specific case have a name?

Liquid adhesion ...

Has it ever been used for something practical?

...is used in some gutters

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It's called the Coanda Effect, and is a consequence of velocity shear due to viscosity. The molecular layer in contact with the surface, has essentially zero velocity (surface referenced), and the velocity increases with layer thickness, the resulting layer to layer drag difference creates a couple that causes the flow to curve around the surface. It is used in aero-plane flaps to curve the air flow down to increase lift. Even flames will flow around a nearby surface. You can watch them in your fireplace.

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