```Date: Nov 14, 2012 1:08 PM
Author: kirby urner
Subject: Re: How teaching factors rather than multiplicand & multiplier<br> confuses kids!

On Wed, Nov 14, 2012 at 12:25 AM, Robert Hansen <bob@rsccore.com> wrote:<< snip >>> Common Sense: Draw a curve without lifting the pencil.>> Formal Reasoning: What does that actually mean and why is it significant?>> Bob HansenWhen I was in high school, they had this symbol, a little open circle(not colored in) that you could put in a graphed (x,y) line to show adiscontinuity. "No defined value of y for this value of x" is what itmeant.  So you could draw like f(x) = x * x (parabola) and then "shootit full of holes" by undefining the function for x = 0.71, 1.95 and -3- -- if you felt like it.What instruments and controls might we count as "continuous" versus"discrete"?  There's a correspondence with our concepts of "analog"versus "digital".  Digital instruments are quantized.  Most dashboardinstruments are "analog" if they have needles.  Gas tank, speedometer- -- we usually think of these as "continuous" i.e. you can apply theintermediate value theorem and say:  if I went from 40 mph to 60 mphthen I must have passed through every possible speed in between, atleast briefly.In the case of what's in your gas tank, we could talk about Avogadro'sNumber and how many moles of a polycarbon (refined crude oil) you aresending through your cylinders.  In metabolizing or combustingmolecules, you are engaged in a discrete activity and your gas gaugecould be said to be measuring a discrete number, just like grains ofsand come in discrete numbers.Computers are said to be discrete devices, but then so are films andvideos discrete.  Around 24 frames / sec is sufficient to create asensation of continuity i.e. no gaps in the action.  Frame rates of 30and above are common.  The color value of each pixel is controlled bysome 32 on-off toggles, or 255 * 255 * 255, where each integer 0 <= x<= 255 is represented by 8-bits.  Red, green blue (RGB).Playing with RGB to control pixel colors is something to do early andoften in math class, if you have any access to recent technology.Pixels are another good example of discrete entities given theappearance of continuity or "analog smoothness".  This will inspiresome students to ask whether perceived reality might be considered"discrete" at some level as well, and in terms of rods and cones,neurons firing (or not) the answer is yes:  there's usually a way totake any analog phenomenon and model / represent it in digital terms.Kirby
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