Huff off: Straw houses are stronger than you were told…
aterials science is everywhere, and you’ve been learning about it for longer than you’d think.
The first little pig built his house out of straw; the second out of sticks; but it was the cunning third pig, a bricklayer, who taught us all an important lesson about materials selection. In reality, however, the Big Bad Wolf would have dizzied and passed out long before first house succumbed to his huffs and puffs.
Straw houses have been built since the Paleolithic Era on the African plains, and have seen spikes in popularity since – the invention of the mechanical hay baler saw a straw-bale construction craze towards the end of the 19th century, and more recently there has been something of a revival, as alternative materials are considered to improve sustainability.
Straw is an excellent insulator. On top of that it’s cheap, easily available and – an increasingly important word – sustainable. The BaleHaus at the University of Bath, which was opened by Kevin McCloud in 2009, was built as a research project in collaboration with industrial partner ModCell, using straw and hemp bale panels. This nifty short video explains the basic principle.
As well as demonstrating fantastic thermal and acoustic performance, in a simulation using hydraulic jacks, the BaleHaus was successfully tested for its resistance to hurricane-force wind levels up to 193kph (120mph). That’s a big set of wolf lungs.
You dropped something: This flamboyant chap had better watch his step – that doesn’t look like toughened glass to me…
In a more tongue-in-check scientific evaluation of fairytale lore, Antariksh Bothale, a mechanical engineer in Bombay, asked ‘What qualities would the glass in Cinderella’s slippers need to have in order for her to walk and dance comfortably (and hold her weight)?’
Bothale’s investigation is a bit of fun, but an impressively thorough one. He considers the yield strengths of different forms of glass compared with the comparative stresses that would develop in the material under Cinderella’s estimated maximum weight of 50kg.
Bending glass: Assuming her stepping angle is around 30°, Bothale claims only half of Cinderella’s weight (500 sin 30) would act in the normal direction of the heel…
His studies accounted for the bending that would be applied to her heel causing compressive stress, the increased impact force when she runs out of the castle as midnight approaches… after contemplating all of this and more, Bothale settled on thermally toughened glass to take Cinders to the ball, recommending that she stick to a toe-first foot strike. Take a look at his full assessment here – it even sparked some comment-based debate.
By Simon Frost