What is the relationship between buoyancy and density?
Buoyancy is the balance between two densities.
The relative density of two objects or compounds determines the amount of observed "buoyancy". This can be a direct effect of immiscible things (lava lamps, rocks in water) or the relative volumetric effect, such as boats.
One favorite exercise:
If a man is in a boat filled with large rocks floating on a lake, and he throws all of the rocks overboard into the lake, does the lake level increase, decrease, or stay the same?
The correct answer is an example of the inter-relationship of density and volume, and how they may affect buoyancy.