Final answer:
Water displacement is used to determine the density of an irregular object by measuring the volume of water it displaces and dividing the object's mass by this volume.
Step-by-step explanation:
Water displacement is a common method for determining the density of an irregularly shaped object or material. To find the density of such an object, its mass is measured by weighing, and then its volume is determined by submerging it in water and measuring the amount of water displaced, typically using a graduated cylinder. The density can then be calculated by dividing the mass by the volume. This method is based on the principle that a substance denser than water will sink and displace its own volume of water. For example, to find the density of rebar, you would first weigh it and then submerge it in a graduated cylinder partially filled with water, noting the rise in water level to calculate the volume the rebar displaced.