A colleague, who hadn’t come across these lessons before
learned what a great resource they can be.
He used Best Circle with his Yr 11 group.
The group learned more about circles, specifically that a
circle is the shape that bounds the maximum area for a given perimeter.
One pupil in the class is a bit of a programmer: he took
things further. That afternoon he
created a webpage (written in javascript) where you can draw a circle and it
will tell you how accurate you are. Brilliantly,
this gives a percentage and features sad/happy kittens to show you how
impressed the feline world is with your effort.
My colleague put it up on his website.
The page is here.
A couple of weeks on he turned it into an iPad app, which
can be downloaded for free here.
He learned that maths can be rather cool!
And me? Well I saw
yet another example of why sharing is so important, whether it is ideas,
experiences, materials or iPad apps!
How do the
programs work?
Well, first of all they join up the line that is drawn so
it forms a closed shape. Then it measures
the perimeter and the area of the shape.
From this it calculates the radius you would get if the perimeter
were the circumference of a circle and the radius you would get if the area
were the area of a circle. Then it
divides the latter radius by the former one and gives the percentage.
Questions:
1] Can you get
close to 100% ?
2] Can you get close
to 0% ?
3] What happens to
the area if you draw a shape that crosses itself (such as a figure of 8) ?
Here are two alternative methods for giving a percentage
score for the accuracy of a circle:
Method A] Assume
the perimeter drawn is that of a circle and work out the radius of the
circle. Use this to calculate the area
of the perfect circle. Compare that to
the actual area drawn.
Method B] Assume
the area drawn is that of a circle and work out the radius of the circle. Use this to calculate the perimeter of the
perfect circle. Compare that to the
actual perimeter drawn.
4] What is the
link between the answers the two methods give?
5] Which one is
equivalent to the method used in the app?
6] Which method is
better and why?