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Floating and Sinking

An object will sink if the upthrust is less than the weight.The object will accelerate downwards to the bottom of the container as there is a resultant force.An object will float if the upthrust is equal and opposite to the object's weight.The object will be in equilibrium as there is no resultant force.When an object is placed in water, it sinks till it displaces enough water such that the weight of the water displaced is equal to the object's weight.When it reaches the point where the upthrust = weight, the forces are balanced and there is no resultant force.

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Specification: Edexcel Physics (8PH0), AS-level, Topic 4: Materials, statement 50. Topic: Fluids.

Key terms in this lesson

upthrust
The upward force exerted on an object submerged, fully or partly, in a fluid, equal to the weight of fluid displaced.
equilibrium
A state in which the resultant force and resultant moment on an object are both zero, so it has no tendency to accelerate or turn.

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