It seems strange because you would think that more legs on a stool or chair would make it more sturdy or stable but in fact not!.

The reason actually lies in the fact that it only takes three points to define a plane.

Any point that is added to that plane will make it harder and harder for the plane to be stable.

__Here's a great activity to show this concept:__

Your fingers will represent points and the paper will represent a plane.

- Take your thumb, index finger, and middle finger and try to put a piece of paper on top of them
- You should notice that any way you place your three fingers the paper will always uniquely lie on all three points.
- Now add a fourth finger by having a new person use their index finger as a new point.
- Notice how hard it is to exactly fit the paper on the plane.
- A tripod for a camera (Click here to see a photo of one)
- A tripod for a transit (this is an instrument surveyors use)

### Triangles are so sturdy/stable becuase they will always define a plane. no matter where the vertices of the triangle lie.

What are some real-life objects that use this knowledge to be more sturdy/stable?

Move to the next section called "The rigidity of a triangle" to learn another neat fact about triangles.

Go to The Rigidity of a Triangle### Return to Main Page