Sci: Bubbles

Without science, technology, engineering, arts and mathematics, there would be no humans, just some smart apes. You can’t have one without the others, because they all emerge from our human curiosity and they feed our curiosity—and one of the things that excited the wonder and curiosity of my granddaughters, before they were two, was bubbles.

As a mid-20^th century child of old-fashioned parents, I learned a lot from Pears’ Encyclopaedia, a compendium that was the Wikipedia of its day. This sturdy volume was prepared under the name of the makers of Pears’ soap, one of whose advertising marks was Sir John Millais’ portrait of his grandson, Willie James. The boy later became Admiral Sir William Milbourne James, GCB, and he had an agile and clever mind, but even as an admiral, his nickname was the painting’s title: Bubbles.

Sir John Millais, a portrait of his grandson, later called Bubbles.

Bubbles bring joy, delight, wonder and curiosity, though some of the bubbles that follow have fairly unusual shapes.

First: a bubble mix recipe

I got this from a friend, who said to mix these ingredients very thoroughly:

* Three parts concentrated detergent (‘Morning Fresh’ or ‘Dawn’ work well);

* Seven parts warm water;

* One part sugar or glycerol (it helps the bubbles to last longer).

My friend added these notes:

* Bubble mix keeps well in an airtight container;

* It works better if it is at least two weeks old, and it lasts for years;

* Hard water isn’t very good for making a bubble mixture;

* Don’t let the mix soak into furniture or the carpet, so use it outside;

* If you ignored that, vinegar can help clean it up.

Odd-shaped bubbles

The first thing you need to do is to make some gadgets to shape some unusual bubbles, and that involves the tricks of the wire-bending trade that you will see in the pictures that follow. Note that these are suggestions, not rules. Play with any and all ideas that you find in this book:

* At the ends of each piece of wire, there is a turned-over bit that I use for joining wires;

* When I have a plan needing a number of pieces of the same length, I wind the wire around a ruler;

* If I want round shapes, I use a broom handle or a small cylinder to make neat circles;

* I join wires by wrapping them around each other and then crimping them with pliers.

Now let’s try a cube, two pyramids and a helix. To make the photos as clear as possible, I used 2 mm aluminium wire, sold as bonsai wire, but you get better bubbles with thin, cheap galvanised tie wire, which is easier to find and cheaper.

1. The cube

What is the natural shape of a bubble? To find out, you need some detergent or soap, a piece of soft wire, a pair of pliers, a pair of wire cutters and a dish. From these, you will gain an unexpected answer.

Safety note: It is possible to cut off short sharp bits of wire with wire cutters, but watch out: the cut-off bits often fly around, making a danger for eyes, and also for small children and pets. Safety goggles are essential for you and any helpers, and watch where the bits go. Clean them up!

Follow the diagrams below to make a cube with a wire handle (a bit like a Cubist frying pan). Sink this into the soap solution, pull it out, and check the shape of the bubble formed.

To make the frame, I used a ruler to measure out a number of similar lengths, as shown in picture 1. I also needed the pliers and cutters shown in picture 4. There are eight lengths of 3.5 cm, then a longer piece that makes a handle, all in one single length. Then as shown in picture 4, there are three more 3.5 cm pieces, each with short bent ends for crimping.

Bubble frames, a helix and making a wire cube with 3.5 cm sides, and a wire handle.

2. A square pyramid

This has the same shape as the Egyptian pyramids (but smaller): a square base, 3.5 cm on a side, and four triangular sides. I made the sides of the triangles about 5 cm long, but 6 cm would have been better.

Notice that there are just two pieces of wire in the construction of the pyramid, and notice also the allowances made for crimping on the ends.

To finish off, I cut a separate long piece of wire to make the handle, using it to crimp together the apex (top) of the pyramid.

A square pyramid

3. A triangular pyramid or tetrahedron

This one is easy to make, because the construction takes just two pieces of wire, using the same methods as before. Play with it!

A triangular pyramid and handle from two pieces of wire.

4. The helix

Use any convenient cylinder to wind the helix and bend the very end into a short U shape that you will later crimp down to make a tight join. The crimping is done with the pliers.

The main thing is that you now have a closed loop that can hold a bubble.

Making a helical bubble.

Stretch the helix out, and cut the wire to leave a straight ‘tail’, about 20 cm long. This passes back through the middle of the helix, and the other end crimps onto it.

When you lift the helix out of the bubble solution, a bubble will be formed, joining the spiral to the central strand. But helical bubbles or spiral bubbles?

To be precise, the shape you will see is a helix, and you have made a helical film that is really a single-sided bubble, if you like. The 19^th century engraving below probably explains it more easily than words, and it also tells us this isn’t new science. The image comes from my Dover edition of C. V. Boys’ classic book, Soap Bubbles, first published in 1890.

From C.V. Boys, page 49.

If you stop and think about it, the helical bubble is no more surprising than the flat bubble you get in a circle of wire. Once again, the effect of surface tension (we’ll come to what that is, later) is to make the surface area as small as possible, stretched between the boundaries. Since the outer wire is a helix, the bubble must be spiral as well.

Did you get shapes like these?

Before we look at the shapes of bubbles, I want to look at some other round things, like balloons, lead shot and rain. The basic question: why are so many things roundish?

Balloons filled with helium may float upwards in the air, but air-filled balloons compress the air inside, and when you add in the weight of the balloon, the whole thing weighs more than the same volume of uncompressed air. Those balloons don’t float, and as we will see later, bubbles are also filled with slightly compressed air. Bubbles don’t float, either, though they are easily caught by breezes.

Fine balls of lead form when molten lead is poured through a copper sieve, at the top of a high tower called a shot tower. As the droplets fall, they change their shape, almost magically, into spheres, and they harden, at least on the outside, before they land in a cooling water bath. Nobody would suggest that lead shot floats, but as it is forming, lead shot falls more slowly than a larger lump of lead, because of air resistance. Remember the spherical shape…

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