Learning to start small in Cabri3D

I was interested in AbsentCat’s Active Geometry post, talking of a “geometry processor” doing wonderful things, but learning to use it sounded too much to cope with in the endless pressure of a school day. I work with young teenagers who should be in early Key Stage Four, but, because their previous education has been disrupted by events beyond their control or a teacher’s capacity to imagine, are in most cases struggling to master KS2 or even KS1. How could this active geometry business help them or me? But, during a staff development workshop, I was shown the ready made examples accompanying a copy of the three dimensional version, Cabri3D, mentioned by Philip Yorke. One of them addressed a topic which I was due to tackle with my youngsters: the nets of a solid. When I expressed interest in that example, I was offered a short loan of the laptop on which the workshop demonstration had been run.

Very uncertainly, I rigged up the machine and waited for my class. And they loved it. They are very videogame savvy, and related to the direct manipulation of an onscreen object in a way they had never related to paper or cardboard equivalents. The software allows them to pick up a single section of the flattened net, swing it along a guide path, and have the attached panels follow it. The cube assembles itself. Then a face can be swung back, restoring the 3D solid to flat net. As many times as they wish. With the ice broken, they were then amenable to physical exploration in a way that they had never been before.

Since then, I have read Chandra’s account of her Beanbag Thrower - another example of starting small, with a simple and manageable aspect, not being overawed by the greater power available. I have learned a lot from the experience, and learned a lot too from her account. Next time, I shall be bolder - integrating the software into a lesson plan, as she has, rather than just starting with it. I have borrowed the demonstration machine again, and next week I shall be using the 2D version, Cabri II Plus, for a more ambitious project around bicycle wheels. I intend to watch the demonstration videos, have signed up for another workshop on geometric software in CDT, and plan to spend the summer reinventing myself - bring it on.

[contributed by BobTheBumbler]

Graph magic!

Magic is a stage in the developmental history of science — a history which each of us retraces as we grow to intellectual maturity. Its study as such by eight-year olds was designed to meet criteria in cultural history and imaginative creation, but also as a context for strengthening critical faculties. The ability to rationally assess likely and implausible explanations of phenomena makes great strides at this age; separation of reality from model is central.

A link between mathematical models and spells, illustrated by Omnigraph, was well received and opened up a riot of speculative theorising. It also offered a new stage on which to parade the key concept of the algebraic “placeholder”.

Omnigraph is a graph processor, with facilities for investigating a number of mathematical areas up to very basic calculus. Equations or Cartesian coordinates, entered from keyboard or menus, are instantly reflected in curves, lines, points and shapes drawn in the graph window. Or, looked at another way, “spells” in the lower window produce magical results in the upper one - but rules can be deduced, even at this age, to predict the result of any given spell.

The mouse changes scaling, draws tangents, normals, areas, and the rest; curve drawing can be paused or abandoned, and in many cases the equation/spell is displayed as the mouse passes over a line.

A quadratic spell produces a passable model of the path followed by Harry Potter’s broomstick as he swoops to aid a Quidditch team-mate before returning to his normal altitude position. We can also play the part of the villainous Quirrel, interfering with the spell to alter Harry’s flight: alter one part of the spell (the m coefficient) to induce suicidal recklessness; change another (the constant c) to pull him out of the dive earlier - or cause him to crash!

If it looks like I’m getting carried away - well, perhaps I am. There is nothing more inspiring than watching young minds leap over their fears and years to grasp an idea. By the end of the morning, any member of the class could evaluate the value of y for any x, plotting the results on a graph paper Quidditch field. They could also deal implicitly with negative values for m and c, expressed as subtractions in a modified “spell”.

We assembled a tolerable Cartesian cartoon representation of Nearly Headless Nick, behind a transparent acetate screen overlay carrying a Hogwarts map. The pupils derived great amusement and insight from altering transformation matrix-spells to move Nick about the castle, expand him, shrink him, distort him in various ways…

Omnigraph is a simple, no frills program in its interaction with the user, which makes it very transparent in use. It is also well known; all the teachers involved had encountered it, if not used it, before. For more advanced work it could be replaced by Autograph; this would sacrifice instant usability in favour of added options. Both programs work well in conjunction with graphical calculators, for teaching at the levels where those are appropriate. Autograph offers stronger tools (eigenvalues, for instance), enhanced display options and statistical data plotting.

[Contributed by AbsentCat]

Active geometry

Formalised geometry can seem a meaningless set of hurdles. “To do geom” observes Geoffrey Willans’ schoolboy antihero, Nigel Molesworth (Down With Skool, 1958), “you hav to make a lot of things equal to each other when you can see perfectly well that they don’t”. Dynamic geometry software such as Cabrie-Géomètre II (CG2), a program developed in France and powered by the backing of calculator manufacturer Texas Instruments, offers the solution. It is an excellent platform for investigating detailed aspects of the Autograph models — as preliminary learning in advance, as subsequent consideration of observed phenomena, or as both in a refinement loop.

CG2 is a geometry processor adding to axiomatic Euclidean geometry the active, participatory element of transformational or analytic geometry. Here is an opportunity to discover for oneself, in a hands-on way, where the axioms came from. It allows fundamental components (points, lines, shapes) to be combined and moved in ways which obey geometric definitions. If a line is defined as a tangent to a circle at a particular point, for example, then the circle, line and point can all be freely moved around, the circle resized, and so on, but the line will remain tangential to the circle at that point. Additional constraints can be used for particular purposes, as can slider controls. A number of ready-made examples are provided, ready for instant classroom use. During our trial a physics teacher borrowed it and used two lines, a circle and an ellipse to demonstrate both the inverse square law and the cause of eclipses in a single pass.

At every stage, the software encouraged rapid explorative investigation whilst also pegging the mathematical representation back to a concrete reality comprehensible to the pupils.

[Contributed by AbsentCat]