Lockdown Challenge: Kleenex clocks and geodesic domes

Aaahh, tea! And a biscuit! There’s nothing like a biscuit to dunk in your tea. Or, if you are in the land of Stars-and-Stripes, a doughnut to dunk in your coffee. But hidden in these edible delights are some secrets of physics like surface tension, viscosity and more. And, believe it or not, a clock. Look closely at the dunking process. Biscuits don’t go soggy all over at once. The tea soaks in, going further every second – until after a minute or so... in it goes, to the bottom of the mug. A longer running version of this mini-saga is to take a strip of tissue paper and get water going along it in a controlled way, making a kind of clock.

Cut a strip of blow-your-nose-on-it tissue 8-10mm wide and 15-20cm long. Use a water-soluble felt-tip pen to put coloured dots along its length. Then stick a piece of clear cellotape-type sticky tape over it and under it, so that the tissue is wholly within the tape, but sticking out at the ends. Not quite as good, but easier to do, is to tape the tissue to a waterproof surface so it is encapsulated (the tape stops evaporation).

Now dunk one end into a wide bottle cap, as seen on plastic milk containers, sticking the rest down to a flat surface if it isn’t already. Put your Kleenex Clock to run horizontal or uphill a little: maybe a 1 in 25 slope. Now pour water into the cap. Water soaks into the tissue, going further and further along as time passes, the coloured dots disappearing and colouring the water as it goes along. Your Kleenex Clock is now running – probably for 15 or 30 minutes – but not ticking!

How far the water does the water go with time? Mark off the distances that are run at 15 minutes, 30 minutes, 1 hour, 2 hours: does your Kleenex Clock run predictably? Does it run faster or slower as it carries on? If you put time v. distance on a graph is the line straight? Or a bit of a curve?

Try your Kleenex Clock more uphill. Does it run slower? And try it with tissue that’s thicker or thinner.

The Kleenex Alarm Clock

Can you find a battery, some wires, and a beeper? Then you can make yourself an electric Kleenex Clock: a Kleenex Alarm Clock!

A Kleenex Alarm Clock has two bared wire ends, not quite touching at the top of the tissue strip. Water goes in as before, but when the waterfront arrives at the far end the water provides a conductive path in a circuit. A pinch of salt between the wires increases the water conductivity making the beeper work better.

You will need a battery like a PP3 with a connector-clip or wires to tape over the terminals, or a battery box. Also a piezo beeper/sounder/buzzer. Make sure that it goes beep when a battery is connected: some only beep with AC. Amazon and electronic suppliers like Rapid or Farnell sell beepers for a pound or so.

Your Challenges

1. Make a Kleenex Clock run for a whole 8 hours.
2. Make a Kleenex Alarm Clock that will run for 8 hours and wake you up in the morning. You need never oversleep again!
3. Make a clock out of another microporous/fibrous material. What about cotton cloth or paper or even a piece of string? Hint: some materials would be fine, but are ever so slightly greasy: they will only work if you add a tiny bit of washing-up liquid to the water.

And finally… can you make your Kleenex Clock do something physical like snap a mousetrap, ring a bell, launch a ball with an elastic band? Hint: when tissue paper gets soggy, its strength goes down – especially toilet tissue of course!

If you liked this, you will find lots more seriously fun science stuff in my 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.

Lockdown Challenge #28 - Make your own geodesic dome

Renowned inventor, designer, architect and systems theorist, Buckminster Fuller, was born on 12 July 1895, 125 years ago.

Fuller was the President of Mensa from 1974 to 1983, wrote over thirty books, coining or popularising terms such as synergetics (the study of systems in transformation) and tensegrity (the characteristic property of a stable three-dimensional structure consisting of members under tension that are contiguous and members under compression that are not).

He is primarily remembered though, for popularising the geodesic dome. This is a spherical form in which lightweight triangular or polygonal facets consisting of either skeletal struts or flat planes, largely in tension, replace the arch principle and distribute stresses within the structure itself.

Fuller envisaged that they’d improve human shelter, but they have more often been used on military radar systems, churches, sports stadiums and auditoriums. It is, however, possible to build your own geodesic dome. It would make an ideal summer gazebo or greenhouse and because of its structure, more able to withstand the elements than the average traditional models.

You’d need lots of pieces of plastic tubing or wooden poles. If you want something a bit smaller, toothpicks and matchsticks

3D Design software, for instance, SketchUp, to work out how many pieces you’d need depending on the size of your dome. From this, you can calculate the length of the dome’s struts and the number of hubs, which connect the tubes together to form the structure.

You can buy custom-made hubs online. They look like the sort of thing you see on a gazebo, but have six connectors.

If you’re making your own, you’ll need to take into account the part where they connect to the struts, when working out the length needed.

For a wooden dome, you could also use laminated blocks with hinge joints for the hub and wooden beams for the struts.

If using toothpicks or matchsticks, plasticine or gumdrop sweets will work as hubs.

For any cutting, use a saw stand with stops for accurate measuring. Marking up hundreds of pieces of wood or plastic tubing will take a very long time.

If using plastic for struts and your own hubs, don’t forget to drill holes in the pipes so you can bolt them to the hubs.

Lay out a base ring of struts and connect each together using the hubs to raise the first tier.

Start attaching additional pentagon-shaped rings from each connector in the hub.

Put in the base poles, and add a hub to every third set: you end up with poles pointing upwards and meeting together in the point of a triangle.

Then start adding the pentagons to create the dome. Alternatively, you can build the dome strut by strut, hub by hub. Depending on the size, you’ll need a ladder if you do it this way.

Take out a section of tubes at the front to make the door.

If you’ve made it out of wood, it’ll be a bit more complicated and require some sawing and drilling to create a frame that enables you to get in and out without affecting the stability of the structure.