Shear thinning and yield stress of complex fluids

Can liquids change their viscosity due to applied shear forces?
In this demonstration, we place weights on top of a syringe filled with various fluids used in everyday life.
1) Air: First, we calibrate the required weight to overcome the syringe friction.
2) Water with blue food colouring: The rate at which the fluid flows is proportional to the weight.
3) Honey: Although very viscous, the rate at which the fluid flows is proportional to the weight, similar to water.
4) Ketchup: We see a yield stress threshold followed by the shear thinning of the viscosity so that the fluid flows faster.
5) Toothpaste: We see an intricate behavior characterized by the interplay of yield stress, shear-thinning, and viscoelastic features of this complex fluid.

The demonstration is prepared for the course "Advanced Topics in Non-Newtonian Fluid Mechanics - 036104," taught by Assistant Professor Evgeniy Boyko at the Technion-Israel Institute of Technology in Winter 2024.

Music: bensound.com
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