Buoyancy and density are two related concepts in physics. Density refers to the mass of a substance per unit volume, while buoyancy refers to the ability of an object to float in a fluid. An object will float in a fluid if it is less dense than the fluid, and it will sink if it is more dense than the fluid.
Buoyancy is based on Archimedes' principle, which states that the buoyant force on an object in a fluid is equal to the weight of the fluid displaced by the object. This means that if the weight of the fluid displaced by an object is greater than the weight of the object, the object will float. If the weight of the fluid displaced by an object is less than the weight of the object, the object will sink.
The relationship between buoyancy and density is important in many areas of science and engineering. For example, in shipbuilding, it is important to ensure that a ship is designed so that its weight is less than the weight of the water it displaces, in order to ensure that it floats. Similarly, in the design of hot air balloons, it is important to ensure that the balloon is less dense than the surrounding air in order to ensure that it floats.