The property of certain gels or fluids to become less viscous when sufficient energy in the form of impact force or vibration is applied to overcome its yield stress is known as:

Thixotropy — The property of certain gels or fluids to become less viscous when sufficient energy in the form of impact force or vibration is applied to overcome its yield stress; at rest they require a specific time to return to the previous viscous state. Key Concept Both pseudoplasticity and thixotropy are shear-thinning processes; the difference is that changes in pseudoplastic viscosity do not exhibit the time dependency characteristic of thixotropy. Ref: Phillip’s Science of Dental Materials ed 12 pg 152