Teacher2Teacher |
Q&A #1834 |
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Hi Stephanie - when I teach changing units, I include dimensional analysis as one of the ways to do it. I think the key is to relate the process back to concepts the students are familiar with - in this case proportions and multiplying by 1, because that's what you're really doing when you multiply by the conversion factor. For example, suppose I need to change 254 cm to m. My conversion factor is 1 m ________ . Kids always wonder why I picked this form. 100 cm I model it by thinking out loud: "I need 2 equivalent measurements (so the fraction equals 1) that contains cm and m. I know 1 m = 100 cm and I need the cm in the denominator so the cm units will be the fraction 1 (divide out). I need to check that I'm using a conversion that really equals 1 and that I'll get m left when I divide everything." 1 m 254 cm x 1 m 254 cm m 254 cm x ------ = -------------- = --- x --- x --- 100 cm 100 cm 100 cm 1 = 2.54 m If you haven't tried modeling the process out loud and relating it back to multiplying by 1, you might try this. It usually works for my students. -Jenny, for the Teacher2Teacher service
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