Sang froid

Dau.II came home for feeding this last weekend.  (And no, she didn't bring a sack full of laundry for her mother to process: she's been better trained)  Her visit has been good for my rather sad efforts to Get Down With The Hood and relate to my students - she can tell me about the fads that are sweeping through Cork this Fall.  Cork is a little behind, say, Los Angeles in trendiness but is still a good stretch ahead of us here in the Boondocks. I was intrigued to be shown a youtube compilation of a peculiar sub-class of Epic Fails where the drive wheel of a motorbike is held against the rim of a play-ground round-about while teenagers try to hold on.  It wouldn't be an Epic Fail if they didn't fly off, hit their heads off the motor-cycle or carry away the cameraman.  Like all EFs it is both excruciating and guiltily hilarious. A common feature is where the spinning dude looses his hand-grip and promptly flings out over the edge of the carousel to make a couple turns with head and torso horizontal until his feet have to let go.

Hanging out in this way should slow the whole shebang down in the exact reverse of those spinning figure skaters who go faster when they bring their arms into their sides. The record is in excess of 300 rpm or, briefly, 5 revolutions per second.  As you know, I failed my Physics "O" level, so I couldn't explain why this works without help.  It's because the angular momentum (L) is the product of inertia (I) x angular-velocity (w):

L = Iw

where the inertia is mass x square of the radius

I = mr^2

or to meld the two formulae

L =  m * r^2 * w

the mass of the system (m) and the angular momentum (L) must stay constant, so if you decrease the radius by bringing in your arms and the spare (horizontal) leg then w the angular velocity must increase.

"Inertia" made me have another go at trying to find some evidence of soldiers trying to stop a cannon-ball with their feet and having their leg torn off for their pains.  I was sure I'd read such an account, associated in my mind with the Battle of the Alma in the Crimean War.  There's a discussion here, which wasn't there when I last looked, about being foolish with 'spent' cannon-balls.  One of the commentators offered a telling image of a sledge hammer being seen to move rather slowly but you really really wouldn't want it to make contact with your knee. In 2011 Mythbusters fired a traditional cannonball at some water barrels.  It missed and flew off through a residential neighborhood of Dublin CA perforating several walls, flying straight through a house,bouncing off a roof and finally lodging inside a minivan. You don't want to try catching that sort of ball.

Cannon-balls inevitably makes me think of Henry Paget, the Earl of Uxbridge who behaved like a demon-hero at the Battle of Waterloo charging about and the saving the day at a crucial juncture.  As evening fell and the tide of battle was turning against the French, Uxbridge was was sitting on his horse next to the Duke of Wellington when he cried "By gad, sir, I've lost my leg", to which the Duke replied "By gad, sir, so you have".  The sang was never froider than in that generation of British soldiers.  There is a famous tombstone to Paget's leg near Waterloo in Belgium.  He was 47 when this mishap occurred but lived on for another 38 years.  After that you couldn't call Paget tough as old boots but you could say he was tough as old boot.

Paget and Wellesley inevitably make me think of a collateral relative of mine Lt Col T. Scientist.   He died at the head of his regiment - the 94th Foot - this month 200 years ago at the crossing of the Nivelle on the French side of the Pyrenees at the end of the Peninsula War. According to my father, a minor shoot on a branch of horse-riding cannon-fodder from King's County, my middle name is in honour of this chap.  He was 30 when he pegged out: promotion came thick and fast if you were anything like competent and you survived.  William Napier the historian of the War cited him thus:
"In him also were combined mental and bodily powers of no ordinary kind. A graceful symmetry combined with Herculean strength, and a countenance at once frank and majestic, gave the true index of his nature, for his capacity was great and commanding, and his military knowledge extensive both from experience and study. On his mirth and wit, so well known in the army, I will not dwell, save to remark that he used the latter without offence, yet so as to increase his ascendency over those with whom he held intercourse, for though gentle he was valiant, ambitious, and conscious of his fitness for great exploits. He, like Freer, was prescient of, and predicted his own fall, yet with no abatement of courage. When he received the mortal wound, a most painful one, he would not suffer himself to be moved, but remained watching the battle and making observations upon the changes in it until death came. "

That's a long roundabout from a merry-go-round!