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One of the reasons triangles are important is because they are strong shapes. A triangle can't be pushed out of shape in the same way other polygons can. (Remember, a polygon just means a shape with straight sides.)
Look at the square. Try moving the red dots with the mouse, and you will see the square can be squashed into a diamond shape (called a rhombus) without any of the sides bending or changing in length.
Now try it with the pentagon. ('Pentagon' just means a polygon with five sides.) Look how many different shapes you can make, all without bending the sides or making them longer or shorter. Can you turn it into a star?
This is not possible with a triangle. Once the length of the sides is set, its shape can't change. Try it!
Try this out for yourself with some pop-sticks or pencils. Use rubber bands to join them together at the corners to make a square, a pentagon and a triangle. Now try squashing them. Take a piece of paper and write down what you found out. Make sure you draw some pictures of what you did.
Copyright Glen Prideaux,
2002.
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