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Engineers use a few shapes again and again. A triangle frame cannot change shape unless a side changes length, so it is rigid — that is why roof trusses, electric pylons, crane arms and bicycle frames are full of triangles. A square frame with loose corner pins wobbles until a diagonal brace splits it into triangles; a frame with n sides needs n − 3 braces. Arches carry loads by squeezing their stones together, beams carry them across a gap, and domes spread them in all directions.
✓ You passed this lesson’s test.
Triangles stay put — “a triangle cannot change shape; other frames need diagonal braces”
Use it for: Straw and newspaper tower challenges, building model bridges and spotting shapes in buildings.
Check: A hexagon frame needs 6 − 3 = 3 braces to be rigid ✓
▶ Watch it animatedWork it out in your head or on paper, type the answer and press Check. Stuck? Press “Show me how”.
Right: 0 · Tried: 0
20 questions. Check each answer, then go to the next one. Get 16 or more right to pass.
🏅 Sign in with Google to earn the 🔺 Triangle Builder badge when you pass — and a certificate when you finish all 8 lessons of Part 3 · Structures and materials. You can still take the test without signing in.
Why does it work? When should you use it? Ask in English, मराठी or हिंदी.
Sign in with Google to ask Free — 20 questions a day.
Prefer a real teacher? TalentJR teachers take live online classes anywhere in India and visit homes in selected cities. Tell us what you need and our team will call you with timings and fees.