Find Density

An object's density is defined as its mass per unit of volume. Density is used in geology, metallurgy and other physical sciences as an identifying property of rocks, minerals and metals and in calculations for an object's buoyancy in a given liquid to determine if it will float in that liquid. To figure an object's density, follow these steps.

Steps

Finding Density

  1. Determine the object's mass. An object's mass, simply put, is how much stuff it contains. You can find the mass by weighing the object with a balance or spring scale.
    • If the object is to be held in a container while being weighed, such as a liquid or powder in a graduated cylinder, the container must first be weighed empty so that its mass can be determined and subtracted from that of the object inside the container.
  2. Determine the object's volume. An object's volume is how much space it takes up. Volume can be determined in one of several ways, depending on the object:
    • If the object is solid with regular dimensions, measure its length, width and height (or length and diameter if cylindrical) and calculate its volume mathematically depending the shape of the object. There are different formula for finding the volume of a rectangle, a cylinder, a pyramid, and so on.
    • If the object is solid and non-porous with no regular dimensions, such as a jagged rock, you can determine its volume by immersing it in water and measuring the volume of water it displaces. (Under Archimedes' principle, an object displaces a volume of liquid equal to its own volume.)
    • If the object is a liquid or powder, place it in a graduated cylinder and read the mark to which the substance fills the container. (If the substance is a liquid, read the mark at the lowest point of the curve the top of the liquid forms.)
  3. Divide the object's mass by its volume. This value is the object's density and expresses it in units of mass per unit of volume. For example, for a 20-gram mass that takes up a volume of 5 cubic centimeters, the density is 4 grams per cubic centimeter.

Using an Example

  1. Write down the problem. Let's say the problem states, "Find the density of a book with a mass of 49 grams and a volume of 7 cubic centimeters."
  2. Write down the mass. The mass is 49 grams.
  3. Write down the volume. The volume is 7 cubic centimeters.
  4. Divide the mass by the volume. 49 grams รท 7 cubic centimeters = 7 g/cm3.

Tips

  • Related to density is specific gravity, which compares the density of an object to that of water. Because the density of water is 1 gram per cubic centimeter, if the density of an object is measured in the same units, the numeric value of its specific gravity will be the same as its density but without the unit after it.

Things You'll Need

  • Balance or spring scale
  • Ruler or measuring tape
  • Calculator
  • Graduated cylinder (for powders or liquids)

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Sources and Citations

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