Showing posts with label dynamic geometry. Show all posts
Showing posts with label dynamic geometry. Show all posts

Saturday, 29 June 2013

Ancient Greek Geometry

Year 5G had a look at a great game, where the object is to create shapes with the classical "straight edge and compass" techniques: http://sciencevsmagic.net/geo/ It's author is Nico Disseldorp.

What's so good about this is that:
  • It's a game! How this geometry should be. Maybe how it was for the ancient Greeks before someone wrote it all down and it had to be "learnt".
  • It constrains you. You can only put your lines and circles in certain places. You have to follow the rules.
  • It starts easy and gets harder, and records your progress.

We had a go with physical rulers and pairs of compasses first. We created all sorts of precise diagrams, and deviated off to some really beautiful ones that some of the children wanted to finish off at home.

by Amandine
But, with the kind permission of the people who'd done some of the pictures that weren't quite right (and it's OK to make mistakes in this classroom) we looked at how they were wrong. After all, these are not uncommon mistakes, and understanding them helps us understand something about knowledge itself. Here's one attempt to make a regular hexagon (it's in pencil so it didn't scan very clearly):
We could see here that the problem was that although the bottom points had been arrived at by finding the precise place where the circles cross, the top ones were, well, guessed at. You might call this kind of guess an informed opinion; we wanted something closer to a fact.

This one used the circles to draw all the points of the hexagon:

This is a lot closer to regular, but suffers from a lack of precision in the drawing.

So, armed with these reflections, we all managed - sometimes it took several goes, and tuition from those who got there first - we all managed to draw a good regular hexagon.

Then we went on to the Ancient Greek Geometry game / puzzle. Here we were helped to get over the problems of drawing by hand by being forced to be precise and to define points with known lines and circles.

One of the interesting things was that ten year olds can be quicker than their teacher! Jose showed Mr Gregg how to do the square, and Sophie showed him a quicker way of doing circle pack three!

Wednesday, 12 June 2013

Mathematics is Everywhere

Douglas Butler
On Monday 10 June 2013, Douglas Butler paid a visit to The International School of Toulouse. He joined the mathematics department for the day visiting lessons and delivering a session to our Year 9 students. Douglas, a world renowned mathematics educator and great advocator of the use of technology in the mathematics classroom, was impressed by the students, the quality of teaching and learning and the facilities at the school.  The Year 9 students, the school principal and myself enjoyed his whizz-bang lesson that I’m calling “Mathematics is everywhere!” The students used Google Earth to skip around the world and visit some places of mathematical interest. Here’s a summary of some of the fascinating discoveries we made.

The Exmouth Hexagons


Zoom in to Exmouth Penisula in Western Australia and discover these strange hexagons in the ground. What transformations could you apply to one to get the other?Why are they there?



Washington Airport


At each end of every runway you may notice different numbers. At Washington Airport there are numerous different runways. Why is there a 4 at the end of one of the runways and the number 22 at the other? On a second runway you will find the numbers 15 and 33. What is the mathematical significance of these numbers and if the third runway has 19 at one end what number will you find at the other?





Melbourne Airport


Continuing on the theme of airports we used Google Earth to look at the elevation profile of the runway at Melbourne Airport. As mathematics teachers we are acutely aware how easy it is to misinterpret graphs – it is important to study them with a critical eye. Looking at the following graph what might you conclude about this runway?
Elevation of Melborne Runway
Unless we look carefully at the axes we might be misled into thinking that the runway is quite steep. Using graphing software carefully we can see that the gradient of the straight line is not at all steep and that planes can land quite safely at Melbourne Airport!

Denge Sound Mirrors

Denge Sound Mirror, Kent
Returning to Europe there exist some wonderful parabolic structures in Kent. Before the invention of radar, the Denge Sound Mirrors  were intended to provide early warning of enemy aeroplanes crossing the Channel towards Britain. This mirror is shaped like the graph of a parabola (y=x² is the simplest parabola) and this was critical  in their efficiency of amplifying the sound.  Where would you stand to best hear the sound? Just like flat mirrors, the angle of incidence equals the angle of reflection. The animated gif below might give you a clue as to why they were so efficient. 



You can find all the resources created by Douglas Butler for his visit here.