## Section 2: Standards of Measurement

The standard system of measurement used by scientists around the world is known as the International System of Units (SI). SI units are easy to use because this metric system is a decimal system of units based on a scale of multiples of ten. Each unit is ten times larger than the next smallest unit and one-tenth the size of the next largest unit.

To measure the distance between two points, scientists use **length**. The size of the object being measured determines the unit that it will be measured in. For example, the length of a football field is measured in meters whereas a pencil would be measured in centimeters.

**Mass** is the amount of matter in an object. The mass of a basketball is outweighed by the mass of a bowling ball.

The **density** of an object can be calculated based on its mass and volume. **Volume** is the amount of space taken up by something. Water displacement is one way to determine the volume of a solid. When an object is placed in water, the amount of water it displaces is the volume of the object. From the mass and volume of the object, its density can then be calculated.

**Time** is the interval between two occurring events which can be measured by a stopwatch or a clock.