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The effect of size and weight

Why can small lizards run about so well on land, with legs that stick out at the sides – while large crocodiles make such a meal of it?

We’re up against a fairly fundamental problem of ‘scaling’ here. It applies to animals, engineering, model-making, you name it.

If you double the size (length) of something, in general you make it eight times as heavy.

You can check this out very easily; using kids’ building blocks, packs of butter or whatever.

Take one block, then place more round it until you have an edifice that’s the same shape but twice as big. That’s to say, twice as long, twice as wide and twice as high. You’ll need 8 blocks to do it (2×2×2, or 2³).

If you want to make your edifice 3 times as big, you’ll need 27 blocks (3×3×3, or 3³).

This causes all sorts of problems. It make elephants slow lumbering beasts compared with lizards.

It means that model-makers have to cheat, to make their parts strong enough. And so on.

Of course, if you’re making something hollow like an aeroplane then things are different. But we won’t go into that.