David was kind enough to send me the Litre Cube from his store (along with some other GREAT items...seriously, check out the store), and I promised to review it. It got me thinking about the importance of these kinds of teaching tools and I thought I'd share my ideas about it with the listserv.
--- The Base Ten Litre Cube by SI Manufacturing, available from MetricPioneer.com, is a precision-made object and a perfect hands-on introduction to the SI – the most successful system of measurement in the world. The litre cube puts units of mass, volume and length literally into your hands. It has 10 millimetre graduations in three directions, physically demonstrating the connections between length, area and volume. Together, they reveal a simple but very powerful relationship placed at the heart of the metric system in 1795: a cube ten centimetres on a side is one litre, and one litre of water has a mass of one kilogram. This holds true even if we scale up or down: 1 millilitre of water is one gram. A thousandth of a litre (1 mL) is a thousandth of a kilogram (1 g). Likewise, one thousand litres of water is one cubic meter, and weighs one tonne. There are technicalities, of course—atmospheric pressure, purity and temperature of the water, and so on—but even after 220 years, in an age when the meter is defined by the speed of light, this relationship is still accurate to a fraction of one millilitre. The litre cube is a vital tool for teaching SI at any level from grade school measuring to high school physics. Not only does the litre cube teach scientific principles of reproducibility and accuracy, it can also teach the practical applications of the SI weight of water. The real strength of the SI, of course, is that in addition to industrial and scientific precision, it’s also extremely user-friendly in commerce and at home in the kitchen. I’ll close by showing how critical this relationship is in a very important practical application where I live in the Sonoran desert of southern Arizona, where temperatures regularly soar over 40 °C and (to quote *Dune*) “water *is* life.” An oft-quoted formula is that a person should drink half their body weight in pounds in fluid ounces per day. A 200 lb person would therefore drink 100 fluid ounces. That is to say, 3 quarts and half a cup. Because a gallon is 128 ounces and (to calculate pack weight) hikers know that a gallon weighs about 8 1/3 pounds, they’ll calculate 100/128 fluid ounces * 8 1/3 pounds at about 6.5 pounds. The same operation in SI goes like this: your body needs, at rest, 33 mL/kg per day. A person who weighs 91 kg will therefore need (91 * 0.033 L) a minimum of 3 L of water, or about 3 kg of pack weight. People should know SI. In science, industry, commerce, at home and in recreation, its use is superior to any other type of measurement. The best way to teach is to show: and the best way to show off the litre and the kilogram is with a hardworking, well-made litre cube like this one from MetricPioneer.com. Eric Shuman
