Kayella

Kayella pours a ribbon of shampoo, and it leaps back up off the heap.

The Physics

Shampoo is shear-thinning: the faster it is sheared, the runnier it gets. A falling stream builds a heap, cuts a dimple in it, and slides out of the dimple on a thin, highly sheared lubricating layer, leaping back up. Each leap lasts about a second before it collapses.

η = K γ̇^(n−1), n < 1

• η: apparent viscosity (Pa·s)
• K: consistency index (Pa·sⁿ)
• γ̇: shear rate (1/s)
• n: flow index (dimensionless; below 1 means shear-thinning)

A. Kaye described it in 1963, and Versluis et al. explained the stable effect in 2006.

Honest caveat: It is not an elastic bounce: the stream slides out on a lubricating layer.

On the shirt

Front: Kayella, the pixel-art character, with the title. Back: the power-law viscosity, the dimple-and-slide mechanism and the 1963 and 2006 sources. Printed on a unisex tee.