Upthrust - GCSE Physics Definition

Upthrust is a force that acts on an object when it is placed in a fluid, like water or air. It pushes upwards against the weight of the object. This happens because the pressure is greater on the bottom of the object than on the top. This difference in pressure creates the upward force called upthrust. When upthrust is equal to the weight of the object, the object will float. When upthrust is less than the weight of an object, the object will sink. Understanding upthrust is important when studying buoyancy and why things float or sink in fluids.