# How can I calculate the buoyant force of a floating object?

May 12, 2015

Use Archimedes' principle, that states something of this nature: "The buoyant force acting on an object immersed in a fluid is equal to the weight of the fluid displaced"

Say, you take a cube of wood(for example) and place it in a bucket of water. Your cube is bound to sink, until, the upthrust force equals its weight.

Where does this upthrust come from?
As the cube sinks, it displaced some volume of water(if the bucket were full you would see water pouring out)

Archimedes simply stated that: $\text{Upthrust} , U = m g$

$\text{density(rho)" = "mass(m)"/"volume(V)}$

$\implies m = \rho V$

$\implies \text{Upthrust} , U = \rho V g$

So if you know the volume of the fluid that was displaced, then you can calculate the Upthrust on the cube.

Note that the volume of the fluid displaced equals the volume of the object iff the object was totally immersed in the fluid.