Lockdown Challenge: A cool construction with ice
Image credit: Neil Downie
As ‘Beast From The East II’ blasted in from the continent in mid-February, Neil Downie took inspiration from it and devised a project to make an Eiffel Tower from ice. Not an easy task as ice is a lot more difficult to work with than you might think. However, in the space of a week, the weather in the UK has turned positively spring-like, but there is still time for winter to bite back. So if it does, here’s a chilling project to bring out the locker.
Lockdown Challenge #38: Building with ice
“Science is magic that works” – 'Cat’s Cradle' by Kurt Vonnegut.
We’ve all made a snowman, right. So why not make an Ice Tower? Snow is pretty easy to make things out of… unless it’s icy. By contrast, ice is surprisingly tricky!
Most materials, if you look closely, are complicated: molecules, crystal structures, shear modulus, Young’s Modulus… But ice is SUPER complicated. There are whole books just on the physics of ice. Ice forms 18 different crystals, which inspired the ‘ICE IX’ in Kurt Vonnegut’s classic sci-fi 'Cat’s Cradle'. It expands as it freezes – that’s the opposite to everything else. It has the lowest coefficients of friction. It is brittle right up to its melting point – it doesn’t soften. So don’t drop it – it will smash! And yet it flows. Yup, only slowly, but it does, even though it’s solid – that’s why glaciers move. And ice is the key to so many things on Planet Earth: the Ice Ages, the weather because clouds are mostly made of ice, and the massive problem of global warming.
OK, it’s tricky, but how do you make an Eiffel Ice Tower? Well, first freeze your ice. Find lots of moulds. The easiest is 2-litre soda bottles and the paper-thin plastic boxes used for things like mushrooms or salad. Just fill them up and put them in the freezer. Too much for the freezer? Put your moulds outside to freeze. Put them far from buildings and trees, with a wide view of the night sky. This is so that under clear skies your warmish water can radiate infrared light to the coldness of outer space and get cold, even on a night without really cold air. At an air temperature of 3°C, you get freezing in this way, although nights of -2°C or less are needed really.
Ice all frozen? Then get the ice out of the moulds. With mushroom boxes, use warmish water on the outside of the mould. With bottles, cut the ends off with a saw, then start a cut with a knife and peel the plastic off the cylinder of ice. Bear in mind the ice is sticky as well slippery. Touch cold ice with damp fingers and you – or your gloves – may stick.
Image credit: Neil Downie
Now it’s time to start building. You’ll need firm ground (or bricks or stone). Bear in mind that ice is not strong. And your ice will have many small cracks and weaknesses. So thick is good. With nothing above, the top can be thinner, but the base, with the whole tower weight above, needs to be thick. Paris style, Manhattan style, or Pagoda? Your choice!
Image credit: Neil Downie
Ice bricks can be most easily shaped with a coarse cheese grater. Keep the tower vertical and the joints horizontal with a spirit level. To join the bricks, make sure that you have matching flat surfaces, and then glue the parts together with a layer of ice-cold water. After a couple of minutes, the bricks will be stuck by ‘ice superglue’. Ice-shavings from the grater can be used to fill some gaps, followed by liquid water, to form a thicker (although weaker) bond. If in doubt, dribble a little extra water in to ensure that gaps are bridged. Over 2m and you will need a step ladder – but be careful.
Image credit: Neil Downie
How tall could an Eiffel Ice Tower be? Large towers are sometimes made in winter festivals like Harbin, China. It’s all down to strength/(density x gravity). With maximum ideal strength of only 1MPa tensile, 10MPa compressive, the maximum height of ice towers of constant cross-section can be ‘only’ 100m or so. But 100m is 30 storeys! By making a tower that reduces in cross-section means exponentially taller towers without exceeding the strength.
Properly frozen, ice is an insulator. So why not freeze some LEDs into your tower. A great centrepiece for a banquet!
If you liked this, you will find lots more fun science stuff in Neil Downie’s books, like ‘The Ultimate Book of Saturday Science’ from Princeton University, and for lots of other things (and a free copy of the ‘Exploding Disk Cannons’ book), visit www.saturdayscience.org
There is also the back catalogue of Lockdown Challenges from 2020 to choose from if you are looking for more options. The IET also has a host of resources that adults can use to engage children with the world of STEM.
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