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Term used to describe a specific behavior of suspensions. For example, when shear forces act on a liquid that contains spherical particles in high packing density, the particles move away from each other before they start to slip. This phenomenon can also be observed in densely filled paste. Based on the total amount of particles, this represents an increase in volume due to the shear forces. Osborne Reynolds gave this phenomenon the name dilatancy. (O. Reynolds, Philosophical Magazine, Vol. 20, 1885, p. 469). In dense suspensions, flow resistance also increases under the action of shear forces. When walking on a wet sandy beach, the sand expands beneath the feet, stores water in its interior and then acts like dry sand on the surface. This is an effect of dilatancy as well. Dilatant originally means "extending itself" and refers to an expansion of the molecular interstices which changes the shape of a body and makes it grow in volume. In a broader sense, dilatancy describes an increase in viscosity as a result of shear forces. Such a fluid has a dilatant movement.