Power is the rate of doing work or the rate of converting energy. A unit of work or energy is called a joule. A person doing 4,000 joules of work in four seconds would be doing work at a rate of 1,000 joules per second. A joule per second is called a watt (W) in honor of James Watt, inventor of the steam engine. Hence, the person developed a power of 1,000 watts. When a hundred watt light bulb is lit, electric energy is converted to heat and light at a rate of one hundred joules per second. In the United States, the power developed by engines and motors is usually expressed in horsepower (hp). The horsepower unit was coined by Watt who estimated the rate at which a typical work horse could do work: One horsepower equals 746 watts. In an effort to use metric units for all physical quantities, there...