Density is a crucial concept when it comes to understanding buoyancy. It refers to the mass of an object divided by its volume. In simple terms, it tells us how tightly packed the particles are within an object. When it comes to buoyancy, the density of an object determines whether it will float or sink in a fluid.

To illustrate this, let's consider two objects: a wooden block and an iron block. The wooden block, being less dense than water, will float, while the iron block, being denser than water, will sink. This difference in density determines the buoyancy of these objects.

Another example is a helium-filled balloon. Helium gas has a lower density than the surrounding air, causing the balloon to float in the atmosphere. On the other hand, a deflated balloon, filled only with regular air, would be denser than the surrounding air and would not float.

Understanding the concept of density allows us to predict the buoyancy of objects based on their densities.