Water displacement is a scientific method used to precisely determine the volume of solid objects that have irregular shapes. Unlike standard geometric shapes, which use simple length, width, and height measurements, this technique relies on the principle that a submerged object pushes aside a volume of liquid equal to its own volume. This guide provides step-by-step instructions for accurately performing a water displacement measurement.
Understanding the Principle of Displacement
The foundational concept of water displacement rests on the idea of volume equivalence. When a solid object is fully immersed in a liquid, it occupies space, causing the overall liquid level to rise. The increase in the liquid’s volume, as observed in the measuring vessel, is identical to the volume of the object itself.
This physical law allows scientists to translate a change in liquid level into a precise volume measurement for any non-absorbent solid. This method accurately accounts for surface irregularities that would be impossible to measure with a ruler.
Equipment and Preparation
The measurement requires a few standard pieces of equipment, including a graduated cylinder or an overflow can, water, and the object whose volume is to be determined. A piece of thin string or thread is also helpful for safely lowering the object into the vessel.
Before beginning, the measuring vessel must be placed on a flat, stable surface to ensure the initial water level is read accurately. The initial volume of water is then recorded, reading the meniscus (the curved surface of the water) at its lowest point. If using an overflow can, the can is filled until water just begins to drip from the spout, establishing a known starting level. Overflow cans are particularly effective for larger objects that would not fit easily into a standard graduated cylinder.
The Measurement Procedure
Carefully introduce the object into the measured water without causing a splash, which would compromise the accuracy of the reading. It is often beneficial to tie the object with a thin thread and gently lower it until it is completely submerged beneath the water’s surface. The thread should be thin enough that its volume does not significantly affect the final measurement.
Once the object is fully submerged, the water level will have risen to a new, higher mark inside the graduated cylinder. If using a graduated cylinder, the final water level is read and recorded, observing the lowest point of the meniscus. Ensure no air bubbles are clinging to the object, as these would contribute falsely to the measured volume.
If an overflow can is used, the displaced water is collected in a separate, dry graduated cylinder placed beneath the spout. The object remains submerged until all the displaced water has been collected, at which point the volume of the collected water is measured directly. This final reading is the second piece of data needed for the calculation.
Calculating Volume and Density
Once the initial and final volume readings have been recorded, calculating the object’s volume becomes a simple subtraction problem. The volume of the object is determined by subtracting the initial water volume from the final water volume after the object was submerged. This difference represents the exact amount of liquid the object physically displaced.
For example, if the initial water volume was 50 milliliters and the final volume was 75 milliliters, the object’s volume is 25 milliliters. This volume measurement is a prerequisite for calculating the object’s density. Density is calculated by dividing the object’s mass, which must be measured separately using a balance, by the volume obtained through the displacement method. This yields the density in units like grams per milliliter, providing insight into the material’s composition.