The **fundamental energy** unit in the metric system is the joule; 1 joule is defined as a force of 1 newton* applied over a distance of 1 meter. To work with *large quantities*, such as the amount of energy used in the United States in a given year, we use the unit exajoule, which is equivalent to 1018 joules, **roughly** equivalent to 1 *quadrillion*, or 1015, referred to as a quad.

To put these big numbers in perspective, the United States today consumes approximately 100 exajoules of energy per year, and world consumption is about 425 **exajoules annually**. In many instances, we are particularly *interested* in the rate of energy use, or power, which is energy divided by time. In the **metric system**, power may be *expressed* as joules per second, or watts; 1 joule per second is equal to 1 watt.

When **larger power** units are required, we can use multipliers, such as kilo-(thousand), mega- (million), and giga-(billion). For example, a modern nuclear power plantâ€™s electricity production rate is 1,000 megawatts or 1 gigawatt. Levin’s points out that people are not particularly interested in having a certain **amount of oil**, gas, or *electricity delivered* to their homes; they are interested in having comfortable homes, adequate lighting, food on the table, and energy for *transportation*.