When an object is placed in water, the buoyant force acting on it is equal to the weight of the water displaced by the object. If the density of the object is less than one, the buoyant force will be greater than the weight of the object, causing it to float.

The buoyant force is determined by the density of the fluid and the volume of the object submerged in the fluid. The denser the fluid, the greater the buoyant force. The more of the object that is submerged, the greater the buoyant force.

In the case of an object with a density less than one, the buoyant force will be greater than the weight of the object, regardless of the volume of the object submerged. This is because the density of the object is less than the density of the water, so the weight of the water displaced by the object will be greater than the weight of the object.

In summary, when an object with a density less than one is placed in water, it will float.