Which statement best expresses the main idea?

Triangular arrangements steady many frames by directing forces through members that resist changes of shape. (The text links a triangle’s resistance to shape change with the way truss members guide tension and compression toward supports.)

Why does the author call triangulation a design principle rather than a promise of safety?

Materials, dimensions, and connections can remain weak even when the geometry is sound. (The final paragraph warns that a thin member may buckle and a weak joint may fail, so geometry is only part of safe design.)

In this passage, what does “buckle” mean?

to bend or collapse under a squeezing force (The passage pairs buckling with compression, indicating that a thin member can bend or give way when it is squeezed.)

What happens when a diagonal bar is added to the hinged square frame?

The frame gains two triangles that resist an easy change of shape. (The opening paragraph states that the diagonal creates two triangles whose fixed side lengths prevent the square’s easy sideways shift.)

Why Triangles Steady a Frame: Level 3 Reading Comprehension Questions

A square frame made from four hinged bars can lean sideways without changing the length of any bar. Push one corner, and the angles shift until the square becomes a diamond. Add a diagonal bar, however, and the frame gains two triangles. Their fixed side lengths prevent that easy change of shape.

This geometry helps explain the repeating triangles in roof frames, towers, and crane booms. As a load enters a truss, some members are pulled in tension while others are squeezed in compression. The joined members guide those forces toward supports. A triangle does not strengthen the material itself; it arranges the material so the frame resists bending out of shape.

Engineers still must choose suitable materials, joints, and dimensions. A thin member can buckle under compression, and a weak connection can fail before the bars do. For that reason, triangulation is a design principle, not a promise that every triangular structure is safe. Its value begins with a simple observation: a triangle is difficult to distort without changing the length of one of its sides.

Comprehension questions