Q&A #286

Teachers' Lounge Discussion: Teaching conversion of units of measurement

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From: moe

To: Teacher2Teacher Public Discussion
Date: 2002031405:55:14
Subject: teaching metric conversion of prefixes

Lynn writes: How can I effectively teach so that my students understand this topic on conversion of units of measurement such as cm, m and km? For example: most students find it difficult to comprehend that 715 cm = 7.15 m and 2.12 m = 212 cm It becomes frustrating for me to teach since they cannot understand 1cm = 1/100 m or 1 m = 1/1000 km Would you recommend some great activity that I can carry out to make them understand better? ================= hi Lynn the most effective approach is to introduce the prefixes first. Only the prefixes. this is a conversion of prefixes problem. we get so easily trapped in the Imperial way of teaching with conversion of 'units', in metric it is conversion of 'prefixes'. for a class of grade 3 and up, all these can be learned, yes memorized, in a few minutes symbol factor name ------ ----- ----- Y 10e24 yotta Z 10e21 zetta E 10e18 exa P 10e15 peta T 10e12 tera G 10e9 giga M 10e6 mega k 10e3 kilo h 10e2 hecto da 10e1 deca 10e0 = 1 d 10e-1 deci c 10e-2 centi m 10e-3 milli u 10e-6 micro n 10e-9 nano p 10e-12 pico f 10e-15 femto a 10e-18 atto z 10e-21 zepto y 10e-24 yocto i find it useful to present them all at once. i see teachers pick away at this table year after year, let the kids have them all, then they will see what the whole picture is from the start. the important concept to stress is: MEMORIZE THE PREFIX CHARACTER AND ITS ASSOCIATED POWER OF 10. later the kids can learn the name. A brief explanation of what a power of ten means is required. this table should be printed out in non kerned font (monaco) and given to each student to take home and printed in large font for the classroom. copy this table into a word processor, the characters do line up. you might wish to start with the central 7 factors to assure yourself that this material is easily handled you will find that after a quiz given the next day that using visual aids of mm, cm and metre .... mL, cL, dL, L and daL etc that the students will grasp the metric system very quickly. And NO AIDS WITH IMPERIAL UNITS until the class completely understand the metric measures. personally i teach conversion of prefixes with a SINGLE METHOD, BY MULTIPLYING BY 'A FACTOR ONE'. this method works for easy prefix conversion and even better for difficult questions. Difficult conversion like 2 Gm3 = 2 10e? um3 can be done by grade five in a few seconds, and no pencil and paper. the student knows to ignore the metres. they simply say in their mind 9 - (-6) taken three times is -45, so ? = -45 the student would say in their mind: nine minus negative six times three is negative forty five. a work sheet of 30 conversion of prefix questions takes a few minutes. In the past a similar worksheet in the imperial system would take the whole period. By this time one can mix in all sorts of units m2, L, g, Hz, N it doesn't matter, they know to ignore these and just find the 'correct' answer. sorry, about the exponents not showing up properly, this forum & text will not allow them to appear properly, you may have to check this in your printout some comments: fractions are not permitted in the metric system. there should always be a space between the quantity and the unit except for C. Lastly a metre is a unit of measure and a meter is a measuring devise. This make the sentence "the trundle meter measured the distance to be one metre". i would gladly share my materials. enjoy moe2@shaw.ca moe

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