A sphere of iron and another of wood, both of the same radii are placed on the surface of the water. State which of the two will sink if ${\rho }_{iron}>{\rho }_{water}$ and ${\rho }_{wood}<{\rho }_{water}$ where $\rho$ denotes density.

• An object floats on the surface of a liquid when the upthrust or buoyant force exerted on the object by the liquid is more than the weight of the liquid.
• Whereas an object sinks into a liquid when the upthrust or buoyant force exerted on the object by the liquid is less than the weight of the liquid.
• The upthrust of the liquid depends on the density of the liquid.
• The density of iron is more than the density of water, so the weight of the iron sphere will be more than the upthrust due to the water in it; thus, it causes the iron sphere to sink.
• The density of wood is less than the density of water, so the weight of the sphere of wood shall be less than the upthrust due to the water in it. So, the sphere of wood will float with a volume submerged inside water which is balanced by the upthrust due to water.

Therefore, the sphere of iron will sink and the sphere of wood will float.