Why All Faucet Drops Have The Same Shape

Physicists previously theorized that that the angle of water dripping from a faucet right before it breaks off into a drop should be 36.2 degrees. This was true regardless of how fast the water was moving or how the liquid was dispensed.  

Now researchers have confirmed this prediction using high-speed imaging of a dripping faucet.  

The team took more than 200,000 frames per second of a dripping faucet to determine that the angle of a water drop’s cone-shaped neck milliseconds before it pinches off is 36 degrees, according to Science’s Jon Cartwright. 

The study, published in the journal Physical Review E, vindicates previous theoretical studies on how fluids move, which help in many practical applications including inkjet printers.  

The figure below shows the angle for a dripping water droplet:

Water droplet

Photo: Self-similar breakup of near-inviscid liquids/J. R. Castrejón-Pita et. al/Phys. Rev. E 86

And here’s a close-up video of the drop breaking:



Credit: A.A. Castrejon-Pita/University of Cambridge

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