Metric and Unit ConversionsDate: 11/02/98 at 16:06:18 From: Jennifer Corvison Subject: Metrics I am having a hard time figuring out metric conversions. I need an explanation in words. Here are some examples: 60 mi/hr = ______ ft/sec 2 L = _____ oz 7.68 kg = ____ lbs 1816 g = _____ lbs 5 m = _____ in 3 qt = ___ L 10 m(cubed) = _____ ft(cubed) 3 dm = _____ ft 1.4 lb = ___ g Please help. Date: 11/02/98 at 17:17:29 From: Doctor Rick Subject: Re: Metrics Hi, Jennifer. Here are a few tricks that I use to be sure I get conversions right. First, you can write a conversion factor as a fraction that equals 1. For instance, I know that 1 pound = 454 g. I write this as: 454 g ----- = 1 1 lb Second, multiply the measurement you are given by a conversion fraction. Write the fraction so that the units cancel. (You can think of a unit as a number you multiply by, and cancel units in a fraction as if they were numbers.) For instance, to convert 1816 grams to pounds, I write: 1 lb 1816 g * ----- = 4.0 lb 454 g The grams in the numerator cancel the grams in the denominator, so you are left with lb. If I write the fraction as I did above (in my first fraction), the units will not cancel. This is how I know whether I should multiply or divide. Third, if you don't know the conversion factor that you need, you can construct a "chain" of conversion fractions. For instance, here's how to convert 7.68 kg to pounds if I only remember how to convert grams to pounds. First I convert 7.68 kg to grams, then grams to pounds. Here is the full chain: 1000 g 1 lb 7.68 kg * ------ * ----- = 16.9 lb 1 kg 454 g Compound units work similarly. For instance, to convert 60 mi/hr to ft/sec, do this: 60 mi 5280 ft 1 hr 1 min ----- * ------- * ------ * ------ = 88.0 ft/sec 1 hr 1 mi 60 min 60 sec See how miles, hours, and minutes all cancel. Similarly, when you convert m^3 to ft^3 (^ is how we customarily write "cubed" using a keyboard), you want to use the feet/meters fraction 3 times, because m^3 = m * m * m. If you don't know feet/meter (I don't), do this: 100 cm 1 in 1 ft 10 m^3 * ( ------ * ------- * ----- )^3 = 10 * 3.28^3 = 353.15 ft^3 1 m 2.54 cm 12 in If you can use a calculator and you master this technique, you only need to remember a few metric-English conversion factors, such as: 1 inch = 2.54 cm 1 lb = 454 grams 1 liter = 1.06 quart You also need to know the conversions between English units (3 feet in a yard, etc.), and the meaning of metric prefixes (kilo = 1000, centi = 1/100, etc.) I hope this helps you. - Doctor Rick, The Math Forum http://mathforum.org/dr.math/ |
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