Power (noun, “POW-urr”)
In physics, this word describes the rate at which energy is produced, used or delivered. A rate is a measurement of one amount in relation to another. For example, speed is a rate. A car’s speed is the distance it moves divided by the time it takes to move that distance. That gives a rate of kilometers (or miles) per hour.
Power is a rate that describes the time it takes to produce, consume or deliver energy. A battery supplies electrical energy. Its power is the energy it provides divided by the time it takes to deliver that energy. Energy is measured in units called joules. Its relation to time in seconds gives a unit of power called watts. A 40-watt lightbulb uses 40 joules of energy each second.
The word power can also be used to describe energy, usually in the form of electricity, that runs devices and machines. When used with words like solar, nuclear, coal and wind, power describes processes that are used to make electricity.
In a sentence
Scientists made a device that generates electric power from the temperature difference between Earth and the cold night sky.