How can you determine if an object will sink or float based on density?

An object will sink or float based on its density relative to the density of the fluid it's in. If the object's density is greater than that of the fluid, it will sink; if it's less, it will float. This principle is based on Archimedes' principle, which states that any object submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced. Therefore, comparing the densities allows you to predict the object's behavior in the fluid.