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Unformatted text preview: Conversions There are so many units that you can use to express results that you need to become proficient at converting from one to another. Fortunately, there is an easy way to do this and it works every time with no exceptions! You simply multiply by one. (The only question is: which one?) Since 12 in = 1 ft, you can get a one by dividing both sides of the equation by 1 ft, giving 12 in 1 ft = 1 . (Notice that this doesnt say that 12 = 1.) You use this or any similar factor by noticing that if you multiply anything by one, you dont change it. Its easy to see with an example; each factor in parentheses equals one. 1 yr = 1 yr 365 . 24 days 1 yr 24 hr 1 day 60 min 1 hr 60 sec 1 min = 1 / yr 365 . 24 / day 1 / yr 24 / hr 1 / day 60 / min 1 / hr 60 sec 1 / min = 365 . 24 24 60 60 sec = 31556736 sec = 3 . 1557 10 7 sec , where there are only 5 significant figures in the result, because thats the limit on the accuracy of the input data for the number of days in a year. (This is about 10 7 seconds easier to remember.) Another example: 1 mi 1 hr = 1 mi 1 hr 5280 ft 1 mi 1 hr 60 min 1 min 60 sec = 1 / mi 1 / hr 5280 ft 1 / mi 1 / hr 60 / min 1 / min 60 sec = 5280 3600 ft sec . = 1 . 47 ft / sec For an example of what can go wrong, what is one mile in inches?...
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 Fall '11
 Galeazzi
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