Torsional Stiffness for Dummies (WiseGEEK Week 3)

The torsional stiffness of a rectangular frame

Another day of WiseGeek Week, another freelancer babbling through his (her?) chapeau. Much like yesterday's liberal arts major mangling the concept of thermal conductivity, today's DotD candidate also tackled a physical parameter. Please give a warm welcome to WiseGEEK.com's Bobby R. Goldsmith, who gave the world an answer to "What is Torsional Stiffness?" (now languishing at AboutMechanics.com). We just wish it had been the right answer...

For some reason, the notion of "torque" always makes the non-technical among us think of engines... well, those who think of anything at all. So when we run across someone who, like Goldsmith, immediately jumps to rotational systems when confronted with a related word...

"Torsional stiffness is the measure of the amount of torque that a radial shaft can sustain during its rotation in a mechanical system."

...we're pretty sure we found someone rewording a Wikipedia entry or similar text; like Bobby... although not necessarily the right Wikipedia entry. Bobby kept on digging into... whatever it was he was rewording... to add more about torque:

"There are two kinds of stiffness in a rotating mechanical system that is driven by a shaft — torsional stiffness and flexural stiffness..."

Bobby, Bobby, Bobby: what is this obsession with "rotating mechanical systems"? Don't you know that even the flat piece of wood you're using as a bookshelf has an intrinsic torsional stiffness? Torsional stiffness is a property of any material, the property of resistance to twisting by a torque. Snowboards have torsional stiffness. Automotive frames have torsional stiffness. Goldsmith's obsession with rotating shafts bespeaks a complete lack of familiarity with the question.

Want an answer? OK: torsional stiffness, aka rotational stiffness, is a measure of the amount of torque required to produce a unit angle of twist. Its units are Newton-meters per radian. OK?

When someone who knows zilch about the topic attempts to answer a question such as "What is torsional stiffness?" and quickly demonstrates his ignorance – like Bobby R. did here – we're only too happy to hand him a Dumbass of the Day award. Maybe Susan Barwick, his "editor," should get one, too...

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