Mathematics : Geometry Session 1

I was reading the picture book, The Librarian Who Measured the Earth by Kathryn Lasky the other day (See my post on Eratosthenes) and came across some geometry concepts that the boys could not understand.



They could understand why the angle created in the middle of the Earth between the two cities was needed to find the circumference. They just couldn't comprehend how Eratosthenes measured that angle.

I have decided to attempt to give a brief introduction to basic geometry just so they could understand what clever Eratosthenes did to measure the circumference of the Earth without any modern technologyl!

I don't have any curriculum or teaching material to fall back on so I had to just cook something up. Here's what I tried to deliver in our first geometry session.

• I told my boys to draw two intersecting lines.
• Taught them how to use the protractor to measure angles. (eg. measure angle b)
  
• Introduce the terms: acute, obtuse and right angles (I need them to know these because I would be reading a book about Pythagoras soon! He is another Greek mathematician.)
  
• They already knew that 2 right angles make 180 degrees so it was not hard for them to see that two adjacent angles on a straight line make a total of 180 degrees. (eg. a + b = 180) I made them calculate adjacent angles (eg. angle c)
  
• The amazing things was that when I asked them to measure the opposite angle (eg. angle d), D immediately said there is no need to measure because the opposite angles "are the same". My eyes nearly popped out. Wow! This was easier than I thought!

I was tempted to go on and on but appealed to my keener senses and decided that this was enough for a 7-year-old in one session! I left them to happily draw intersecting lines, measure angles and calculate angles while I slipped into the kitchen to prepare lunch. They were amused the WHOLE time!

Now, I will have to think of what I need to teach next...