## Wednesday, January 18, 2012

### Ironing Coffee Filters; No Starch Needed!

 What I should be doing!
When I teach angles or the properties of circles, I find that most children have difficulty cutting out a true circle (even with a blackline).  I have resorted to purchasing cheap coffee filters (not the cone shaped ones) and ironing them flat....much to my chagrin as sometimes these take precedence over my ironing husband's shirts. You can iron several filters at one time, and once they are ironed, they form excellent ready-made circles. Here are some of the ways you can teach angles using these circles.

1)   Introduce the fact that each and every circle contains 360.

2)   Have the students fold their coffee filter in half.  Discuss that this is a straight angle.  Ask, “How many degrees does it contain if it is one-half of a circle?”  (180)

3)   Have the students fold the coffee filter one more time, into fourths.  Talk about this angle being called a right angle and that it contains 90.  Ask, "What fractional part of a circle is this?"

4)   Have the students use this fourth of a circle to locate places in the classroom where it will fit (e.g. the corner of their desk, a corner of a book, a corner of the board).

5)   Explain that these corners are right angles and without right angles, we would live in a crooked world.  Nothing would be straight!

Linking Math and Literature for Older Students

Read Sir Cumference and the First Round Table (A Math Adventure) by Cindy Neuschwander. This is a story about a clever knight of King Arthur’s named Sir Cumference. By using ideas offered by the knight’s wife, Lady Di of Ameter, and his son, Radius, King Arthur finds the perfect shape for his table.  Basic geometric vocabulary involving circles (circumference, radius, and diameter) is introduced. Her book can be found on my bookshelf at the bottom of this blog page. Click on the book for more information.

Want more ideas for teaching angles?  Check out Angles: Hands-On Geometry Activities

#### 1 comment :

Emily Allman said...

The coffee filters are a great idea. I do an activity with my 'first-day' geometry students every year where we find the center of a circle and then use paper folding to explore geometric shapes and their properties. I have always spent hours cutting out circles!