&Bullet; physics 14, 32

Video recordings show that the small mountain of liquid that is created when a drop hits a liquid surface has some surprising properties.

CJM van Rijn et al. [1]
A false color video of the formation of a jet in water with fluorescent particles scattered across it. The time is given in milliseconds. Video is slowed down ten times.

The video of a “jet” – the small tip that forms immediately after a drop hits a larger body of liquid – shows that the top of the structure is initially decelerated with up to 20 times the acceleration of gravity G[1] . This rapid slowdown suggests that surface tension, not gravity, is the driving force behind the shapes of jets.

Cees van Rijn from the University of Amsterdam and his colleagues released individual liquid droplets with fluorescent particles from a height of 8–33 cm above a liquid bath containing the same particles. The researchers tested water, ethanol, and a mixture of glycerine and water. Using laser lighting, they recorded the movement of the particles in order to determine the speed and shape of the jet.

CJM van Rijn et al. [1]
Pull Gis in a jet. The tip of this liquid jet, which is created by a drop of liquid hitting the surface shortly before, is initially decelerated with 20 times the acceleration of gravity G.

The most extreme delay occurred in the earliest moments of the jet, but the delay was noticed G until the jet fell back to the surface. The researchers also found that the beam shape was self-similar, meaning that the shape remained essentially unchanged for most of its existence, except for a time-dependent scaling factor for the horizontal and vertical axes. The researchers developed a theoretical model that was consistent with the data for a wide range of liquid viscosities, densities, and surface tensions. For their next steps, van Rijn and his colleagues plan to carry out similar experiments on the International Space Station or in another low-gravity environment in order to observe the effects of surface tension on the formation of the jet independently of gravity.

– Griffin Wilce

Griffin Wilce is a physics Scientific writing intern.


  1. CJM van Rijn et al., “Self-similar jet development after drop impact on a liquid surface”, Phys. Rev. liquids6th, 034801 (2021).

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