Volume describes the amount of three-dimensional space an object occupies. For objects with uniform, geometric shapes like cubes or spheres, determining their volume involves applying standard mathematical formulas. These formulas use specific dimensions such as length, width, height, or radius to calculate the space enclosed.
However, many objects in the natural world or everyday life do not possess such predictable forms. Irregularly shaped objects, lacking consistent dimensions or symmetrical structures, present a challenge for volume measurement, as their complex contours prevent the direct application of simple geometric formulas. This necessitates alternative approaches.
The Science of Displacement
The principle underpinning the measurement of irregular object volume is fluid displacement, famously attributed to Archimedes. This principle states that when an object is fully submerged in a fluid, it pushes aside a volume of that fluid equal to its own volume. The displaced fluid can then be measured to determine the object’s volume.
The physical space an object occupies in the fluid is precisely matched by the space the displaced fluid once held. Therefore, by accurately measuring the volume of the displaced fluid, one effectively measures the volume of the submerged object.
Step-by-Step Water Displacement
To measure an irregular object’s volume using water displacement, gather a few common items: the object itself, a measuring container with clear volume markings (like a graduated cylinder or a measuring cup), and water. For smaller objects, a graduated cylinder provides greater precision due to its narrow diameter and fine scale. For larger objects, a larger container, such as an overflow can (also known as a Eureka can), might be more suitable.
Begin by filling the measuring container with a known volume of water, ensuring the initial water level is high enough to fully submerge the object without overflowing the container. Record this initial water volume accurately, noting the measurement at eye level to minimize parallax error. Gently lower the irregular object into the water, ensuring it is completely submerged and no air bubbles cling to its surface. Air bubbles, if present, would artificially inflate the measured volume.
Once the object is fully submerged, the water level in the container will rise. Read and record this new, elevated water volume, again at eye level. The difference between the final water volume and the initial water volume represents the volume of the submerged object. For example, if the initial volume was 50 milliliters (mL) and the final volume is 75 mL, the object’s volume is 25 mL.
When to Use and When Not To
The water displacement method is particularly effective for dense, non-porous objects that are safe to submerge in water. Items like rocks, glass marbles, metal figurines, or certain types of plastic toys are ideal candidates. Their inability to absorb water ensures that the measured displacement accurately reflects their solid volume. This technique is also well-suited for objects that are small enough to fit within standard measuring containers, making it a practical choice for many common irregular items.
However, this method has limitations that restrict its applicability. Objects that are porous, such as sponges or certain types of wood, will absorb water, leading to an inaccurate volume measurement as the absorbed water is not displaced. Similarly, objects that float will not fully submerge, making it impossible to measure their entire volume through simple displacement. Very large objects may exceed the capacity of available measuring containers, and delicate or water-sensitive items, like electronics or certain artworks, would be damaged by submersion.