# Bouyant Forces

## Key Questions

The buoyant force is the weight of the displaced fluid.

#### Explanation:

If the object involved sinks, it displaces a volume, V, of the fluid equal to the object's volume, V, when on dry land.

If the object floats, it displaces a volume, V, of the fluid equal only to as much as is under the surface. That volume can be hard to determine depending on the shape of the object.

In either case, the buoyant force, ${F}_{b}$, equals the volume, V; times the density, $\rho$ (in $\frac{k g}{m} ^ 3$) of the fluid; times the value of g.

${F}_{b} = V \cdot \rho \cdot g$

I hope this helps,
Steve

Normally does not vary with depth, unless the object is compressible, or density of fluid varies with deoth

#### Explanation:

Buoyancy or buoyant force is proportional to object's volume and density of the fluid in which the object floats.

$B \propto \rho \cdot V$

So with depth, density may change, or the volums of the object will change when it gets compressed due to the higher pressure at greater depth.

The buoyant force is equal to the weight of the water displaced by the object.

#### Explanation:

The buoyant force is equal to the weight of the water displaced by the object. The buoyant force is an upward force. The object's weight is a downward force. So comparison of the magnitudes of the buoyant force (weight of the water displaced by the object) and the object's weight determines whether or not the object sinks or not. If the object floats, the 2 magnitudes are equal.

I hope this helps,
Steve

• Buoyancy is the upward force acting on an object. For example if you see cork floating on water. Now why does cork floats on water?

It floats on water because the density of cork is less than the density of water.Because the density of cork is less than the upward force the cork floats on water.

Similarly a nail sinks in water because the density of nail is more than the density of water. Because the upward force is less than the density of nail the nail sinks.