What Are the Differences Between the Metric System & the English Measuring System?
- Many cultures have evolved convenient measures for specific purposes. A town is two days away, or a room is 10 paces long, or guests drank two pots of tea. The Imperial system arose in just this way, with myriad specialized units arising from different industries or tasks, or in some instances simple historical accidents. In time these units came to be standardized in relation to each other, sometimes with fairly convenient relations (12 inches to a foot) or sometimes with somewhat less intuitive factors (5280 feet to the mile, originally conceived of as a thousand paces).
- The metric system originated from a desire for more objective, universal standards. Rather than defining a unit of length by the length of an arbitrary king's foot or knuckle, SI originally defined the meter in relation to the circumference of the Earth. Other units were derived from this one basic unit wherever possible. A cubic meter is a unit of volume, for example, but is inconveniently large for everyday purposes, so SI uses the liter, defined as 1/1000 of a cubic meter, or 1,000 cubic centimeters. The SI unit of mass, the kilogram, was in turn defined as the mass of one liter of water.
- SI measures use a system of prefixes indicating power-of-ten factors to create new units. For example, a millimeter is 1/1000 of a meter and a millisecond is 1/1000 of a second, while a kilowatt is 1,000 watts and a kilometer is 1,000 meters. In contrast, the Imperial system uses a host of different conversion factors between smaller and larger units: 2 pints make 1 quart, 3 feet make 1 yard, 12 inches make 1 foot, and so on. Yet Imperial is not immune to the lure of decimal simplicity; the Fahrenheit temperature scale was set to give a range of 100 degrees between a freezing cold day and a scorching hot day.
- As science advances, a better understanding of the relationship between physical concepts emerges. Mass and weight turn out to be distinct but related properties; energy turns out to be just one, despite occurring in a great many forms. Imperial units tend to have been derived from handy equivalents, like horsepower or candlepower, from which conversion factors could later be calculated. SI units, on the other hand, tend to be built up from already defined units. For example, the metric watt (a unit of power) is defined as 1 joule per second, where a joule (the unit of energy) is defined as 1 newton-meter, and a newton is the force required to accelerate a mass of 1 kilogram by 1 meter per second squared. The Imperial unit of power is the horsepower, which happens to be 550 foot-pounds per second, and while the Imperial foot-pound is a derived unit of energy, it can get confusing since the pound is often used as a unit of mass as well as a unit of force.