Volume is the measure of the three-dimensional space an object occupies. For simple geometric shapes like cubes or spheres, this measurement is straightforward, relying on standard mathematical formulas. An irregular object lacks defined straight edges or uniform curvature, making the application of these simple formulas impossible. Its volume cannot be calculated directly from linear measurements alone.
The Science Behind Measuring Irregular Volume
Measuring an irregular object’s volume relies on the principle of fluid displacement. When an object is fully submerged in a fluid, it displaces a volume of that fluid exactly equal to the volume of the object itself. This concept allows scientists to convert a solid object’s volume into a more easily measurable liquid volume.
This method depends on the object being denser than the liquid it is placed in, typically water. Density is the mass of a substance divided by its volume. If an object’s density is greater than water’s density, it will sink completely, ensuring full submersion and accurate displacement. Objects with lower density will float, requiring a modification to the standard procedure.
Practical Steps for Measuring Volume by Displacement
The practical application of displacement requires a container suitable for accurate measurement, such as a graduated cylinder or an overflow can. Begin by filling the container with water and recording the initial water level, designated as \(V_1\). Ensure the water surface, or meniscus, is read at eye level to minimize measurement error.
Next, carefully introduce the irregular object into the container, allowing it to sink completely below the water line. Lower the object gently, perhaps using a piece of string, to prevent splashing, which would skew the final result. The object must be fully submerged without touching the sides or bottom of the container if possible.
Once the object is fully submerged, the new water level is recorded as \(V_2\). This final volume represents the original water volume plus the volume of the submerged object. To isolate the object’s volume, a simple subtraction is performed: the volume of the object is equal to \(V_2 – V_1\).
The result of the subtraction is typically expressed in milliliters (mL), which directly corresponds to cubic centimeters (\(cm^3\)). For accurate measurements, especially with larger objects, an overflow can (or Eureka can) is often used. This device has a spout near the top; once filled to the spout level, any added volume spills out into a separate measuring beaker. The volume of the displaced water is then measured directly from the beaker, eliminating the need to read initial and final levels within a single container.
Handling Objects That Float or Absorb Water
Objects that float present a challenge because they do not fully displace their own volume when resting on the surface. To address this, a “sinker” method is employed, where a second, denser object pulls the floater completely underwater. The volume of this sinker must first be measured separately using the standard displacement method.
The sinker is then attached to the floating object, and the combined volume is measured. The true volume of the irregular floating object is found by subtracting the known volume of the sinker from the measured total combined volume. This ensures the floater is fully submerged while accounting for the added weight.
A separate issue arises when measuring porous objects, such as certain types of wood or absorbent ceramics. These materials absorb water, meaning the liquid volume that disappears into the object is incorrectly counted as displaced volume. This leads to an underestimation of the object’s true volume.
To prevent absorption, the porous object must be sealed before displacement measurement. Applying a thin, waterproof coating, such as a non-water-soluble varnish or plastic film, creates a barrier. This sealing prevents water ingress while only minimally affecting the overall volume measurement, allowing for an accurate reading.