Measuring Matter

Scientists use the International System of Units, abbreviated SI units, for measuring matter. The SI unit for mass is a kilogram and for length is a meter. When measuring volume, the liter is the most commonly used unit. Prefixes are used to indicate smaller or larger units. For example a centimeter is one- hundredth of the length of a meter. SI units enable scientists to measure matter and share data in a consistent and accurate way.

An object’s mass refers to the amount of matter an object contains, while an object’s weight is the measure of the effect of gravity on its mass. The mass of a person is the same on the Moon and the Earth, but the person weighs less on the Moon than the Earth because the Moon exerts a smaller gravitational force than the Earth.

Volume is the amount of space that matter occupies. The volume of liquids and gases are typically measured in liters and milliliters. Solids are often measured in cubic centimeters. One cubic centimeter is equal to one milliliter. To calculate the volume of a solid, measure and then multiply its dimensions. A box with a width of 25 cm, a height of 4 cm, and a length of 45 cm, has a volume equal to 4,500 cubic centimeters. To find the volume of an irregularly shaped object, such as a rock, scientists sometimes submerge the object in a container of water to see how much water is displaced. The rise in the water level indicates the volume of the rock.

Matter can also be described by measuring its density. Density is the mass of an object in a given volume. To calculate density, divide an object’s mass by its volume. The unit for density is grams per cubic centimeter. For example, a piece of aluminum with a mass of 500 g and volume of 200 cm3 has a density of 2.5 g/cm3. A piece of iron with the same volume has a mass of 1500 g. Iron’s density is 7.5 g/cm3.