Dave Rock, age 12, of Hartford, Iowa, for his question:
WHAT IS A WATT?
A watt is a unit used to measure power. It is most often used to measure electric power.
An electric device will use one watt when one volt of electric potential drives one ampere of electric current through it.
The number at the top of a light bulb shows its power requirements in watts. A light bulb operating at 100 volts and using two amperes consumes 200 watts (100 x 2 amperes). Electric power is often measured in kilowatts (1,000 watts).
In the metric system, the watt is used to measure mechanical power. A machine produces a power of one watt if it uses one joule of energy in one second.
The power unit called watt was named after a Scottish engineer and inventor named James Watt. Watt is remembered for an improved engine design that made steam power possible.
Not satisfied with the way steam engines of his time operated, he set about to improve it. He discovered the principal of the separate condenser and patented his idea in 1769.
In the old engines, steam filled the cylinder space under the piston. The steam was then condensed, leaving a vacuum into which the piston was pushed by atmospheric pressure. This meant alternately heating and chilling the cylinder.
Watt reasoned that because steam was an elastic vapor, it would fill any container into which it was admitted. If the steam filled cylinder opened into a separate, chilled container, steam would continually move into the container and condense there, producing the vacuum in the cylinder without having to chill it.
Watt developed crank movements so the engine could turn wheels. He also invented an expansive, double acting engine, a throttle valve, a governor for regulating engine speed and many other devices.
In 1784, James Watt used steam cells to heat his office, and thus became the first person to find a practical use of steam for heating.
The Scottish engineer also did scientific research in chemistry and metallurgy, and was one of the first persons to suggest that water is a compound, not an element.
Crude steam engines used before Watt's time burned large amounts of coal and produced little power. Their lateral, or back and forth motion, restricted their use to operating pumps. Watt's invention of the separate condenser made steam engines more efficient and made it possible for them to receive wide application.
At the age of 21, Watt started his engineering life as an instrument maker at the University of Glasgow.