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Grades K–2 · Machines

Why do builders put triangles inside frames?

A frame can be made from four straight bars joined at their corners. If the corners can turn, a push can make a rectangle lean sideways. The bars can stay the same length while the shape changes.

M45 visual explanationThe push is to the right. The frame with turning corners can lean. A strong bar across the other frame makes two triangles.A bar across a frame makes trianglesTurning cornersWith a bar acrossCan lean sidewaysTwo trianglesStrong bars and joins help keep the shape

In the diagramA bar across a frame makes trianglesTurning cornersWith a bar acrossCan lean sidewaysTwo trianglesStrong bars and joins help keep the shape

With turning corners, the left frame can lean. The bar across the right frame makes two triangles that hold its shape.

A bar across the frame makes two triangles. Now the frame cannot lean in the same way without a bar changing length or a joint giving way.

Builders use triangle shapes in bridges, roofs and tall frames. The bars and their joins still need to be strong. The triangle helps the whole frame keep its shape.

About this explanation

Starting knowledge: Recognize a rectangle and a triangle.

Connect this idea: Structures & Materials

Sources

  • NASA — STEMonstrations: Engineering Design—Trusses
  • NASA — International Space Station Learning Activities: Trusses
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