The shape of a substance does not determine if it will sink or float. It is the average density of the substance compared to the density of the fluid it is placed in that determines whether it will sink or float. An object will sink if its average density is greater than the density of the fluid, and it will float if its average density is less than the density of the fluid. This is known as the principle of buoyancy, which states that the upward force exerted by a fluid on an object is equal to the weight of the fluid displaced by the object.