How shape affects strength: tubes and beams
Design & Technology · Key Stage 2 · The School
The same amount of material, shaped differently
Take the same amount of card. Roll it into a tube, or leave it flat. The tube holds far more weight before bending. No material was added. Only the SHAPE changed. Shape can be as important as material. This is easy to feel with your own hands, without needing any tools at all.
Why a tube works
When something bends, one side stretches and the other side squashes. A solid rod has material sitting uselessly in the middle, where almost nothing happens. A tube puts material at the edges instead, exactly where the stretching and squashing occur, so it resists bending using less material. The middle of a solid rod is doing almost no real work at all.
Beams shaped like letters
An L-shaped or T-shaped beam works the same way. A flat strip of metal bends easily. Fold the same strip into an L shape and it barely bends at all. Building girders are often shaped like an I for this exact reason — most of the material sits at the top and bottom, where it is needed most.
A flat sheet of paper laid across two books sags under a single coin. Roll the same sheet into a tube and stand it on end: it now holds a heavy book. Fold the same sheet into a zig-zag and lay it flat again: it now holds several coins without sagging. Three shapes, one sheet of paper, three very different results — and not one gram of material was added.