Your city’s being attacked by gigantic alien monsters, so you leap into your own 120-metre high mech and go out to do battle. Cool.
It all began in the 1950s with Inoshiro Honda’s Gojira (Godzilla) – a 120-metre tall reptile with radioactive breath – and has been a staple ever since.
Just one problem. It won’t work. Yup, I’m on my hobby horse again. You all think I’m a humble historian and writer with 50 books under my belt. True, and I’ll be on to writing from the next post.
But my other enthusiasm’s science, especially physics. And Hollywood movies…don’t…
In Pacific Rim, the mech issue was controllabilty. Actually the problem is scalability. When you scale an object the mass goes up by a power of three. That’s why horses have skinny legs compared to elephants.
The average Kiwi bloke is 1.77 metres tall and drinks beer. Scale our statistically average beer-drinker up to 120 metres (a factor of 67.79) and you’ll be scaling mass by 311,619. Sure, our mech’s going to be made of carbon fibre and titanium (or something) – but you get the idea.
Mass brings other issues into play too – inertia, momentum and kinetic energy. You can swing your legs and arms pretty easily. But with 311,619 times the mass it’s a different story – and more than just by that figure. The physics are clear:
Momentum – this is linear, sure – it’s MV (mass times velocity)
Kinetic energy – (the energy contained in a moving object) isn’t linear at all – is ½ MV <exp>2. The killer is the exponent.
Moment of rotational inertia (the energy needed to START an object moving, assuming you’re rotating the leg about a pivot in the hip) – also not linear, it’s I = mr <exp>2 – yup, that annoying factorial again, and this time the product isn’t even halved.
See how fast a hummingbird flaps its wings? No. I can’t either. Compare that with an elephant – they can’t flick those legs with the instant acceleration of a hummingbird’s wings.
There is no way you’ll get snappy high-speed mech punches or sprints – well, you could, but the energy requirements and tensile strength of the materials you’d need are huge, and the leverage needed means your mech, design-wise, wouldn’t be a scaled up Kiwi beer drinker at all (actually, this might be a good thing – think of the beer you’d save).
So that’s the physics. Mechs are cool. But they won’t work. Not if they’re shaped like humans. Because – as Sir Isaac Newton tells us – we don’t scale.
So is there a way of creating an exciting super-mech? Sure is…and – well, how can I put it? The mech I have in mind would trash the shiny metal ass of anything in Pacific Rim. Or anything else.
Copyright © Matthew Wright 2013
Coming up next: Serious stuff (promise) – sixty second writing tips, tips for National Novel Writing Month, and ‘Write It Now ‘ – a regular exploration of everything about writing.