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Re: How teaching factors rather than multiplicand & multiplier
confuses kids!
Posted:
Nov 14, 2012 1:08 PM
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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 Hansen
When 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 a
discontinuity. "No defined value of y for this value of x" is what it
meant. So you could draw like f(x) = x * x (parabola) and then "shoot
it 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 dashboard
instruments are "analog" if they have needles. Gas tank, speedometer
- -- we usually think of these as "continuous" i.e. you can apply the
intermediate value theorem and say: if I went from 40 mph to 60 mph
then I must have passed through every possible speed in between, at
least briefly.
In the case of what's in your gas tank, we could talk about Avogadro's
Number and how many moles of a polycarbon (refined crude oil) you are
sending through your cylinders. In metabolizing or combusting
molecules, you are engaged in a discrete activity and your gas gauge
could be said to be measuring a discrete number, just like grains of
sand come in discrete numbers.
Computers are said to be discrete devices, but then so are films and
videos discrete. Around 24 frames / sec is sufficient to create a
sensation of continuity i.e. no gaps in the action. Frame rates of 30
and above are common. The color value of each pixel is controlled by
some 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 and
often in math class, if you have any access to recent technology.
Pixels are another good example of discrete entities given the
appearance of continuity or "analog smoothness". This will inspire
some 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 to
take any analog phenomenon and model / represent it in digital terms.
Kirby
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