### Key Concepts

### 9.1 The Metric System

- The metric system is decimal system of weights and measures based on base units of meter, liter, and gram. The system was first proposed in 1670 and has since been adopted as the International System of Units and used in nearly every country in the world.
- Each successive unit on the metric scale is 10 times larger than the previous one. To convert between units with the same base unit, you must either multiply or divide by a power of 10.
- The most used prefixes are listed in Table 9.1. An easy way to remember the order of the prefixes, from largest to smallest, is the mnemonic
*King Henry Died from Drinking Chocolate Milk.*

### 9.2 Measuring Area

- Area describes the size of a two-dimensional surface. It is the amount of space contained within the lines of a two-dimensional space.
- Area is measured in square meters units; in the metric system the base unit for area is square meters (${\text{m}}^{2}$).

### 9.3 Measuring Volume

- Volume is a measure of the space contained within or occupied by three-dimensional objects.
- Volume is measured in cubic units; the base unit for volume in the metric system is cubic meters (m
^{3}) - The liter (L) is a metric unit of capacity but is often used to express the volume of liquids. One liter is equivalent to one cubic decimeter, which is the volume of a cube measuring $10\text{cm}\u0102\u201410\text{cm}\u0102\u201410\text{cm}$.

### 9.4 Measuring Weight

- Mass is the amount of matter in an object whereas weight is the force exerted on an object by gravity. The mass of an object never changes; the weight of an object changes depending on the force of gravity. An object with the same mass would weigh less on the moon than on Earth because the moonâ€™s gravity is less than that of Earth.
- In the metric system, weight and mass are often used interchangeably and are expressed in terms in grams or kilograms.

### 9.5 Measuring Temperature

- Temperature is a measure of how fast atoms and molecules are moving in a substance, whether that be the air, a stove top, or an ice cube. The faster those atoms and molecules move, the higher the temperature.
- In the metric system, temperature is measured using the Celsius (Â°C) scale.
- The Celsius scale was created with 100 degrees separating the point at which water freezes, 0 Â°C, and the point at which water boils, 100 Â°C. Scientifically, these are the points at which water molecules change from one state of matter to anotherâ€”from solid (ice) to liquid (water) to gas (water vapor).