Triangles & Trusses

The only rigid polygon

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Triangles are the only rigid polygons with hinged corners.
• A rigid planar truss needs at least $2j - 3$ bars.
• In a loaded truss, top members are compressed and bottom members stretched.

Steps

1. Squares wobble, triangles don’t
2. Push on the corner
3. Bracing a gate
4. How many bars?
5. Forces in the bars
6. Steeper is easier
7. Pulled or pushed?