Pitota

Pitota, a tricorn-hatted river engineer, studies water rising in a glass tube.

The Physics

In 1732 Henri Pitot reported to the Paris Academy a bent glass tube he had dipped into the Seine with its mouth facing the current. The water in it stood higher than the river surface, and the extra height measured the flow speed. Bringing the moving water to rest at the mouth turns its kinetic energy into pressure head. He found water near the surface flowing faster than deeper down, overturning the belief of the day.

h = v²/(2g)

• h: rise of water in the tube above the free surface (m)
• v: flow speed (m/s)
• g: gravitational acceleration, 9.81 m/s²

Double the speed and the rise is four times as large. Aircraft airspeed indicators still use Pitot tubes, with a static port.

Honest caveat: The formula is ideal: it ignores viscosity, turbulence and probe shape, and in compressible flows near the speed of sound it needs corrections.

On the sticker

Pitota holds a glass vessel and tube of glowing blue water, with a river behind him. Printed text: PITOTA with the line h = v²/(2g). Pixel-art kiss-cut vinyl sticker, white, in 2″, 3″, 4″ and 6″ sizes.