Where does the term “horsepower” come from and what is the standard for measurement?
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“Horsepower” is a measurement of an engine's rate of doing work. The term “horsepower” was originally coined by James Watt, an English engineer/inventor, in the mid-1700s. Watt focused a great deal of his energy on perfecting the steam engine used in coal mining and for other tasks of the day. In describing his Watt Engines, he compared his engine power to that of a horse that could lift 330 pounds of coal up a 100-foot mine shaft in one minute (or 550 pounds at one foot per second or 33,000 foot-pounds per minute). Over time, “horsepower” terminology was widely adopted as a unit of measure for power. One horsepower is equivalent to 745.7 watts. If you put a one-horsepower horse on a treadmill, it would operate a generator that would produce 745.7 watts.
It becomes more clear if you consider the forces. A horse on a treadmill pulling a bucket of coal up a mine shaft involves linear motion, whereas an internal combustion engine involves rotary motion. With an internal combustion engine, horsepower is calculated as a function of torque and engine rpm (both of which can be directly measured).
What's the difference between drought avoidance and drought resistance?
Drought resistance is the overall ability of a plant to survive prolonged drought. A drought-resistant plant survives drought by drought avoidance or drought tolerance. Drought avoidance, as the name implies, is the means by which a plant delays moisture stress. Plant traits that help avoid moisture stress include deep root systems, number of stomata (leaf pores) per unit leaf area, wax covering of leaves and leaf characteristics.
Drought tolerance refers to a plant's physiological ability to withstand moisture stress. It's ability to maintain cell membrane integrity during moisture stress and maintaining adequate cell water content when tissue moisture stress occurs are examples of drought-tolerance traits.
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