As I walk around a city, I tend to notice the shapes of things.

Check out that elevator shaft up there.

Triangles that are stiffening the structure around it.

That walkway down there has triangles all over it, as does the dock right underneath, actually.

And, of course, huge triangles made out of rope in tension, supporting the masts of that tall ship.

Why do all these structures use triangles?

It's because triangles support, stabilize, and stiffen the structures.

Support, stabilize, stiffen.

Hey, cool, three "S"s. We could make a triangle out of that.

Triangles are really powerful.

To demonstrate how powerful triangles are, I'm going to use a really classic project.

Toothpicks and some gummy worms to join them.

To build a structure that's hopefully strong enough to hold up... ...this brick.

I'm going to use scissors to chop the gummy worms into little gummy connectors.

So I have now a very nice little cube.

I'm going to let it go in three... two, one... (thuds) One of the big challenges we're running into with this particular design is that it's all built out of parallelograms.

A parallelogram is a shape with opposite sides that are parallel and equal in length.

You can see, when you stick the brick on top of this structure, the connectors aren't that strong.

So, instead of staying up, the whole thing just flattens.

(thud echoes) Instead, let's try building a structure based on a triangle.

As I apply force to the triangle, you can see that it has a lot of stiffness.

No flattening this shape.

Four triangles all stuck together.

But the fancy name for this shape is a tetrahedron.

So, I'm just going to keep adding triangles until I have enough structure to support the brick.

Nice.

Those triangles are not flattening like the parallelogram.

The triangles are braced against each other for stability.

It's a nice, strong structure that supports the brick.

Even though the little connectors we used aren't that strong all by themselves.

What a great shape.

You know, when I think about it, I use triangles all the time when I build stuff.

The next material I'm going to work with is some aluminum cans.

The cans are strong in compression, which means they can hold weight when they're pushed on the top and the bottom.

To show how strong they can be, I'm going to stand on one.

And you can see how much load was on it, because all we had to do was tap the side, and it didn't have the stability to resist that tiny, tiny side force, and the whole thing went (mimics crunching).

(crunches) Crushed.

I'm going to build myself a stool out of recycled cans, some duct tape, and paint sticks.

Here's leg number one.

Times two!

Times three!

Times four!

These are going to be the four legs of my stool.

Time for some paint sticks.

I know this isn't going to work out so great, because what shape is it?

A parallelogram.

And this parallelogram, without additional stability, will flatten, like this.

So, I'm going to add some triangles to stabilize it.

Check it out.

A triangle here.

And another triangle here.

Let's see if this thing still acts like a parallelogram or not.

No, it's actually a lot stiffer.

Now I guess all I need is something to sit on top of.

It's still wiggling a little bit.

If I add more triangles, the stiffness of the structure should increase a bit.

Yeah, that's actually a lot more stable.

These triangles in this structure give me those three "S"s-- stability, stiffness, and support.

The stiffness and the stability increased thanks to adding more triangles.

So now the stool can support me.

Any time I'm looking to support, stabilize, or stiffen something I'm making, I'm going to add a triangle.