December 7, 2008

Magic of the links

I WANT YOU to think about your anchor chain for moment. Think about the links. Each link consists of two pieces of rod down the sides, but only one piece going around the top and the bottom.

Now this has worried me for years. If each of the side pieces has a breaking strain of 500 pounds, then the two together can withstand a strain of 1,000 pounds.

But what about the places where the chain bends around the top and bottom? As I said, they're single pieces of rod there, not double. And each piece has a breaking strain of only 500 pounds. So why don't they break when a strain of 1,000 pounds comes on the chain? Is there some sort of magic in play here?

The same principle applies to a length of line going up, through a block, and down again. There are two pieces of line on the sides to take the load, but only one piece running across the top. And yet the line won't break until the strain equals the capacity of the other two lengths of line down the sides.

Now I appreciate that some of you are not in the mood for a puzzle concerning applied physics. Others of you probably dozed off before you got to this paragraph. But, as concerned sailors, shouldn't we be wondering how the heck this works?

I haven't yet found an engineer who can explain this to me in plain simple words of less than four syllables. But over the years I have formed a sort of area of understanding in my brain. From this grey fog of near-comprehension a notion has emerged. And it is this:

The bits of chain or line that run up and down along the sides are under tension when a load is applied. And the single bit on the top is under compression. Not tension, you note. Compression. It's being squeezed down, not pulled apart. And you can squeeze something until it's blue in the face and it won't cry uncle.

According to this notion of mine, the chain or line gradually changes from tension to compression as it goes around the bend. Thus, as it turns, it gets stronger. Yes, each humble, mundane link of chain actually doubles its strength as it curves.

Think about that for a moment. It's one of those little magical mysteries of science that people don't write about or even talk about much because it smacks of the supernatural, and psychic phenomena, and other frightening things.

But on those nights when a howling southeaster is doing its best to snap my anchor chain, I'm always very glad its little links are bewitched.

Today's Thought
If you go directly at the heart of a mystery, it ceases to be a mystery, and becomes only a question of drainage. —Christopher Morley, Where the Blue Begins.

Words of wisdom from Scotland:

“A weel-bred dog gaes oot when he sees them preparing to tae kick him oot.”

1 comment:

Oded Kishony said...

Here's another one you can try to explain. When you have a tire changed and they inflate it to 30 pounds, then they mount it on your car and put the weight of the car on the tire you just inflated to 30 pounds, yet if you were to check the tire pressure it is still 30 pounds. How can that be? Isn't the tire now being squeezed by a 3000lb car?

I'm keeping an eye on you ;-)
Oded Kishony