Trying to find math inside everything else

Archive for June, 2014

Parallel to a Parabola?

A while back, I was working on a lesson about average rate of change and wondered the following question: “Could you use the word ‘parallel ‘to describe two non-linear functions that have the same rate of change/don’t intersect?”

Screen shot 2014-06-18 at 8.53.48 AM

Jonathan’s response, though, made me think about what it actually means to be parallel. Often when you ask students, they will respond “two lines that never intersect,” which I usually push back against because 1) how do you know they never ever intersect? and b) skew lines never intersect, either. So when I explain parallel lines, I use the fact that they have the same slope/go in the same direction as the actual definition, which has the consequence of never intersecting. So I looked it up on Wikipedia.

Given straight lines l and m, the following descriptions of line m equivalently define it as parallel to line l in Euclidean space:

  1. Every point on line m is located at exactly the same minimum distance from line l (equidistant lines).
  2. Line m is on the same plane as line l but does not intersect l (even assuming that lines extend to infinity in either direction).
  3. Lines m and l are both intersected by a third straight line (a transversal) in the same plane, and the corresponding angles of intersection with the transversal are congruent. (This is equivalent to Euclid‘s parallel postulate.)

I don’t think statement 3 was particularly useful to me, but the idea of being equidistant was interesting. A vertically shifted parabola is not equidistant from the original – though they never touch, the distance between them gets smaller and smaller.

So that raised the next question – how do I actually measure the distance between two parabolas at a given point? I asked my boyfriend and he responded, “Well, you definitely need calculus….” And who better to swoop in and help with that than Sam Shah.

Screen shot 2014-06-18 at 8.54.01 AM

So now that I know how to find the minimum distance between two functions, all I need to do is find a function that whose minimum distance to my original function is constant, and then I should have something that you could call parallel.

I made a little Desmos graphs with sliders, to help me visualize the process (click to access):

Screen shot 2014-06-21 at 1.27.13 PM

So I have the equation of the perpendicular line

y = \frac{-1}{f'(a)}(x-a)+f(a)

But that wasn’t really helping me see what the parallel function would actually look like. So then I turned to Geogebra. I needed to make a point on the perpendicular line that was a certain distance away from the function, say a distance of 1. So to figure out the coordinates of that point (x,y), I just used the distance formula, plugging in y from above.:

\sqrt{(x-a)^2+([\frac{-1}{f'(a)}(x-a)+f(a)] - f(a))^2} = 1

That gave me the coordinates of the point that is a distance of 1 away from f(x) at a:

(a + \frac{f'(a)}{\sqrt{1+(f'(a))^2}},\frac{-1}{\sqrt{1+(f'(a))^2}}+f(a))

So I made that point in Geogebra and activated the trace, which gave me this:

Screen shot 2014-06-21 at 2.20.38 PM

Lastly, I thought, well, what exactly is this function that I’ve traced? It looks kinda quartic, but that can’t be, because any quartic like this would intersect the parabola, right? So I tried to write the function for it, using parametric equations. Using f(t) = t^2, I made the parametric equation (t + \frac{2t}{\sqrt{1+4t^2}},\frac{-1}{\sqrt{1+4t^2}}+t^2).

I tried to plug that into Wolfram-Alpha to get the closed form, but it was a mess, so I still don’t really know what the closed form would look like. But who says a parametric form isn’t a solution?

(Here is a Desmos page with a summary of what I’ve done, and some sliders to play with, similar to the Geogebratube page, but with colors.)

Advertisements

The Problem with Gamification in Education

(I suppose I shouldn’t say “the” problem, because there are many problems that I won’t be directly addressing, like extrinsic vs internal motivation.)

I’ve read a lot about gamification in the classroom, and while I’ve often thought about it and borrowed some elements from it, I’ve never gone whole hog. The motivation aspect is one of the reasons, but today, as I started reading Reality Is Broken: Why Games Make Us Better and How They Can Change the World, by Jane McGonigal, I realized there’s more to it.

In the first part of the book, Dr. McGonigal provides a definition of games. A game has four defining features: a goal, a set of defined rules, a feedback system, and voluntary participation. And if you think about gamification, you can easily pick out which of those elements is missing.

Because schooling is mandatory and, if you are taking a particular class, the gamification of that class is also mandatory, gamification of ed itself is not a game. If I gamify my chores by playing ChoreWars, I am choosing to take part in that game (even if the chores need to be done regardless). But if my teacher chooses to use a system of leveling up and roleplaying in my class, it is no longer a game; it is a requirement.

When I tried to think, then, about what in education would best fit these four requires, the first thing that came to mind is BIG, Shawn Cornally‘s school in Iowa. There students choose to participate in some project of their own devising, creating the goal and the voluntary participation. Then it is the school’s job to provide the feedback and the rules.

(An aside on the importance of rules – Dr. McGonigal quotes Bernard Suits who said, “Playing a game is the voluntary attempt to overcome unnecessary obstacles.” The rules are those unnecessary obstacles, and the excellent example given was golf. The goal of golf is to get the golf ball in the hole, but if we did that the most efficient way (walking up to the hole and dropping it in), we would get little enjoyment from it. But by implementing the rules of the game, we make the goal harder to achieve and thus much more fulfilling.)

So the big warning to those who want to gamify their classroom is this: if you require it, it’s not a game, no matter what game elements you include.