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Torricelli's law

Torricelli's law follows directly from Bernoulli: fluid flowing out of a small hole some distance below the surface of an open tank reaches the same speed as if it had fallen freely that height. This holds because the pressure is atmospheric both at the surface and at the outlet.

v = \sqrt{2gh}

outflow speed from a tank

Symbols

$v$	outflow speed	m/s
$h$	height from the surface to the hole	m

Example

A hole is $h = 3.0$ m below the water surface in an open tank. $v = \sqrt{2\cdot 9.81\cdot 3.0} \approx 7.67$ m/s.

Torricelli's law only holds when the hole is small enough that the drop in the surface level can be neglected.

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Part of Fluid Mechanics: Continuity and Bernoulli.