The Probert Encyclopaedia of Science & Technology

UPTHRUST

Upthrust is the upward force exerted upon an object when that object is placed in or floating in liquid. Stone boulders immersed in water have an upthrust on them equal to about two-fifths of their weight, and this explains why boulders can be moved so easily by flood water. In 1952 a flood in Lynmouth, Devon resulted in 20 ton boulders being deposited on the streets. These same boulders, when immersed in water had an apparent weight of only 12 tons.
Research Upthrust