|Stretching and squashing — some basic principles
Even though your gumdrop structures are standing absolutely still, their parts are always pulling and pushing on each other. Structures remain standing because some parts are being pulled or stretched and other parts are being pushed or squashed. The parts that are being pulled are in tension. The parts that are being squashed are in compression.
Sometimes you can figure out whether something is in tension or compression by imagining yourself in that object’s place. If you’re a brick and someone piles more bricks on you, you’ll feel squashedÑyou’re in compression. If you’re a long steel cable attached to a couple of towers and someone hangs a bridge from you, you’ll feel stretched — you’re in tension.
Some materials — like bricks — don’t squash easily; they are strong in compression. Others — like steel cables or rubber bands — don’t break when you stretch them; they are strong under tension. Still others — like steel bars or wooden toothpicks — are strong under both compression and tension.
What’s the big deal about triangles?
As you’ve probably already discovered, squares collapse easily under compression. Four toothpicks joined in a square tend to collapse by giving way at their joints, their weakest points. A square can fold into a diamond, like this:
But if you make a toothpick triangle, the situation changes. The only way to change the angles of the triangle is by shortening one of the sides. So to make the triangle collapse you would have to push hard enough to break one of the toothpicks.
If you want to, you can use your gumdrops and toothpicks to build some strong structures that are made by combining triangles and squares. The pattern on the left is one that’s similar to some used in modern bridge design.
Looking for other triangles in structures around you may give you ideas for other designs you can build with gumdrops and toothpicks.