The density of an object is defined by the ratio of its mass to its volume. The concept of density is used in various fields, from geology to physics, and in many other fields of science. The density is able to indicate, among other things, whether an object can float when immersed in water, that is, when it has a density of less than 1 gram per cubic centimeter. The standard unit of measure for density is g / cm3 (grams per cubic centimeter) or Kg / m3 (kilograms per cubic meter), based on the reference system adopted.
Steps
Part 1 of 2: Identify the Variable Values to Use
Step 1. Measure the mass of your work tools before starting
If you need to calculate the density of a liquid or especially a gas, you will need to know precisely the mass of the relative container. In this way you can subtract the mass of the latter from the total weight in order to identify the mass of the object or element whose density you want to calculate.
- Place the empty container (which can be a beaker, glass jar, or any other container) on a scale, then note the weight in grams.
- Some scales allow you to set the measured weight as "tare". If this is your case, place the empty container on the scale pan, then press the "tare" key so that the weight reading detected by the scale is automatically reset to zero. At this point you will be able to measure the weight of anything you put back in the container, without the mass of the latter interfering in the reading.
Step 2. Place the object whose density you want to calculate on the weighing pan in order to measure its mass
You can weigh it directly if it is a solid or you can use a special container if it is a liquid or a gas. Take note of its mass and, if necessary, subtract the weight of the container you used from the measured weight.
Step 3. Convert the mass to grams if necessary
Some scales use a measurement scale other than the gram scale. If the scale used does not use grams, you will have to convert the weight detected by multiplying it by the appropriate conversion coefficient.
- Remember that 1 ounce is approximately 28.35 grams and 1 British pound is approximately 453.59 grams.
- In these cases, you will need to multiply the detected weight by 28.35 if you need to convert ounces to grams, or by 453.59 if you need to convert British pounds to grams.
Step 4. Calculate the volume of the object under examination and express it in cubic centimeters
If you are lucky and are trying to calculate the density of a perfectly regular solid, you will simply have to measure its length, width and height by expressing these three quantities in centimeters. At this point, simply multiply the three values obtained together to find out the volume of the object.
Step 5. Determine the volume of an irregular solid
If you are working with a liquid, you can use a graduated cylinder or beaker to calculate the volume. If, on the other hand, it is a solid with an irregular shape, to calculate its volume, you will have to use the correct formula or immerse it in water.
- Remember that 1 milliliter equals 1 cubic centimeter. This equation makes calculating the volume of liquids and gases very simple.
- There are several mathematical formulas that allow you to calculate the volume of a rectangular prism, a cylinder, a pyramid and many other solids.
- If the object under investigation is an irregular solid made of an impermeable material, such as a piece of rock, you can calculate its volume by immersing it in water and measuring how much the water level rises due to displacement. Archimedes' principle states that an object immersed in water displaces a quantity of liquid equal to its volume. Based on this information, you can calculate the volume of your object by simply subtracting from the total volume (detected after immersing the object in water) that of the initial liquid.
Part 2 of 2: Using the Density Equation
Step 1. Divide the mass of the object under examination by its volume
You can do the calculations by hand or use the help of a calculator. Calculate the ratio between the mass of the object, expressed in grams, and its volume (expressed in cubic centimeters). For example, if an object weighs 20 grams and has a volume of 5 cubic centimeters, its density will be 4 grams per cubic centimeter.
Step 2. Report the final result using the correct approximation
Normally when real measurements are made, it is difficult to obtain whole numbers, unlike what happens when solving problems at school level. For this reason, when you go to calculate the ratio between the mass and the volume of the object studied, you will get a result composed of a large number of decimals.
- In these real cases, consult the contact person (a professor, your superior, etc.) to find out what precision they need to make the calculations.
- Normally, rounding to the second or third decimal place should be more than enough. Following this rule if the result you got is 32, 714907, you will need to round it as follows: 32, 71 or 32, 715 g / cm3.
Step 3. Understand the significance of density in practice
Normally the density of an object is in relation to that of water (which is equal to 1 g / cm3). If the density is greater than 1 g / cm3, the object under investigation will sink if immersed in water. Otherwise it will float.
- The same relationship is also valid in the case of liquids. For example, oil is known to float on water as it has a lower density than water.
- Specific gravity (or relative density) is a dimensionless quantity defined by the ratio of the density of an object to the density of water (or another substance). Since the units of the numerator and denominator of the fraction are the same, the final result is a simple coefficient that represents a relative mass. Specific gravity is used in chemistry to determine the concentration of a certain substance in a solution.
