Density is a fundamental property of matter that describes how much mass is contained within a specific volume. It measures how tightly packed the material is, defining the concentration of matter in a given space. Finding the volume of regularly shaped objects, such as cubes or spheres, is straightforward using geometric formulas. However, many objects have irregular shapes. For these, a technique based on Archimedes’ Principle offers a simple and accurate solution. This approach, called water displacement, uses the physical law that a submerged object pushes aside a volume of fluid equal to its own volume, allowing the determination of the volume of any solid that sinks.
Necessary Materials and Preparation
Before beginning the measurement process, gather the appropriate scientific tools for precise data collection. You will need a scale or balance to accurately measure the object’s mass in grams. A graduated cylinder is the standard laboratory glassware for measuring liquid volume, though an overflow can or beaker can be used for very large items. You also need a supply of water, which acts as the displacement fluid, and the irregularly shaped object itself.
The object must be completely insoluble in water to prevent it from dissolving. Ensure the scale is properly calibrated and tared to zero, which automatically subtracts the weight of any container placed on it. The graduated cylinder must be dry on the outside to prevent drips from affecting measurements.
The Water Displacement Procedure
The first step is to determine the mass (M) of the dry object. Gently place the object onto the scale or balance and record the measurement in grams, ensuring the reading is stable.
Next, partially fill the graduated cylinder with water to a level that will completely submerge the object without overflowing. Record this initial water level as Volume 1 (V1), reading the measurement from the bottom of the meniscus at eye level for accuracy.
Carefully and slowly introduce the object into the graduated cylinder, allowing it to sink fully until it is completely submerged. Tipping the cylinder slightly or using a piece of thread can prevent splashing, which introduces error. Once the object is resting at the bottom and the water level has stabilized, record the new, higher water level as Volume 2 (V2).
The volume of the object (V) is found by subtracting the two recorded measurements. Calculating the difference between the final water level and the initial water level (V2 – V1) determines the exact volume of water pushed aside. Since the displaced water volume equals the object’s volume, this final number represents the V component needed for the density formula.
Calculating Density and Interpreting Results
With both the mass (M) and the volume (V) recorded, the final calculation uses the mathematical relationship that defines density. Density is calculated by dividing the measured mass by the measured volume, expressed by the formula: Density = Mass / Volume. For example, if an object has a mass of 23.5 grams and displaced 5.0 milliliters of water, its density would be 4.7 g/mL.
The common units for density are grams per cubic centimeter (g/cm3) or grams per milliliter (g/mL). Since one milliliter is equivalent to one cubic centimeter, these two units are interchangeable. Larger-scale measurements often use kilograms per cubic meter (kg/m3).
The resulting number provides insight into the object’s material composition and its physical behavior in water. Pure water has a standard density of 1.0 g/cm3, which serves as a reference point. Any object with a calculated density greater than 1.0 g/cm3 is denser than water and will sink, such as common metals or rocks.
Conversely, an object with a density less than 1.0 g/cm3 is less dense than water and will float. Comparing the calculated density to known values for pure substances can help identify the material of an unknown object.