If you stir really fast, with more shearing force, the PB gets runnier, while if you stir slowly the PB remains stiff. These types of fluids are called non-Newtonian fluids.

In the first experiment, the primary force acting on the ant raft is centrifugal force, per Ko, while in the second, with the vortex, the raft experiences the shearing force.

If you stir really fast, with more shearing force, the PB gets runnier; if you stir slowly, the PB remains stiff. These types of fluids are called non-Newtonian fluids.

For some, like peanut butter, a minimum shearing or cutting force may be needed to get it flowing, and it may vary nonlinearly with shearing strain. Imagine you’re stirring a jar of peanut butter.

This shearing force has never been explained before, and we are the first to identify it,' Backholm says. The complex interactions of fluid and soft matter physics prove challenging to simplify ...