Grades 3–5 · Everyday Life
Why can the wrinkled part of a straw bend?
A smooth drinking straw can kink when it bends sharply. At the kink, the walls flatten together and narrow the passage. A bendy straw has a short section of small ridges and grooves instead.
In the diagramLittle folds make room for a bendEnlarged local folds · not a flow or bend-angle calculationInner side6 units / foldOuter side14 units / foldInner folds close; outer folds spread.The flexible wall can change shape while keeping a passage.
These corrugations give the wall room to change shape. On the inside of a bend, neighboring folds come closer together. On the outside, they spread farther apart. Many small changes share the bend along the wrinkled section, helping it keep an open passage.
The inventor Joseph Friedman developed a flexible paper straw after noticing his daughter struggling to reach a drink through a straight one. Modern flexible straws use different materials and shapes, so their stiffness and how well they hold a bend vary. The enlarged drawing shows the fold idea, not a calculation of how much liquid will flow.
About this explanation
Starting knowledge: Recognize liquid flow, bending and moving parts.
Sources
- Smithsonian Lemelson Center — The Straight Truth About the Flexible Drinking Straw