Enquiring into bubbles

Activities

Bubbles and string
Cubic bubbles
Cylindrical bubbles
Fast bubbles
Lifting with surface tension
Spiral bubbles
A bubble mix recipe

Other related material

Fluids and their behaviour
Surface tension bits and pieces
Other pages on this site

How to do it


Note: if you are looking for science fair or science project areas, this set of Web pages may help you with ideas for techniques you might use: read with a prepared mind! Also, see the projects page.
Cubist bubbles
What is the natural shape of a bubbles? To find out, you need some detergent or soap, a piece of soft florist's wire, a pair of pliers, and a dish.

Use the wire to make a cube with one or two wire handles (a bit like a Cubic frying pan!). Sink this in the soap solution, pull it out, and check the shape of the bubble formed. If you pass the cube through a simple ring carrying a flat film of soap, you can produce interesting effects. Adding glycerine to soap solution makes the bubbles last longer.

Then try the shape on the right, and any other interesting shapes that occur to you, and see what sorts of bubbles form.

This will help you understand


Spiral bubbles
Spiral bubbles? Not really, just spiral films, really, single-sided bubbles, if you like. You need a piece of thick copper wire, about 30 or 40 cm long, a cylinder about 2 cm in diameter, a pair of pliers, a piece of thinner copper wire, and some bubble solution. The photograph probably explains it more easily than words. Wind the thick copper wire tightly around the cylinder to make a sort of spring. Take the spring off the cylinder, and stretch the spring out until it is about 4 cm long. Trim off any rough bits of the wire, and then bend in each end so that it cuts across the centre of the cylindrical space, as shown in the photograph.

Wind the thin wire around one of these end pieces, and pull it through the centre of the stretched spring, before winding it around the other end. When you dip this into the bubble solution, a spiral bubble will be formed, joining the spiral to the central strand.

This will help you understand


Lifting with surface tension
You will need some copper wire in two thicknesses to make a shape like this, where the thin piece of wire is able to slide freely along the Y-shaped piece.

Put a small knob or twist on the end of each of the arms of the "Y", because you will be turning this gadget upside down to lower it into a soap solution, and then lifting it out.

Watch what happens to the slide when you do this.

This will help you understand


Cylindrical bubbles?
Cut two pieces of wire about 40 cm long, and bend them into two circles. Fit two diameter wires at right-angles to each circle, and then join the two "wheels" with a central shaft wire, so they are about 5 cm apart. (When I tried this, I found two wires, twisted around each other, gave far greater stability, and you need to either solder them or glue them with epoxy resin.) If this contraption is dipped in soap solution, a cylindrical bubble will be formed, bowing in around the middle. Experiment with different distances: when you have found the best layout for the soap solution you are using, soldering will make the whole arrangement much more stable.

This will help you understand


Rapid bubbles
You will need some dry ice and some warm soapy water. Dry ice is solid carbon dioxide, and it is very cold: so cold that it is dangerous to handle. Using tongs, take the dry ice and drop it into the water, and watch what happens.

This will help you understand


Bubbles and string
This simple pair of demonstrations will show an unusual side to bubbles. Make a loop of wire about 5 cm across, and add a handle to it, so you can dip the loop into soap solution. Then tie a piece of cotton so it divides the circle roughly in two, but so it remains a little bit slack. Use the illustration on the left as your model for this.

You can also make a section of the thread double, as you can see in the picture on the right.

When you take the first wire loop out of the soap solution, notice how the thread can move around freely in the soap film. Then burst the film on one side of the thread, and notice what happens next. See if you can work out what has caused this effect.

When you have dipped the second loop into the soap solution and pulled it out, burst the soap film between the two threads, and try to explain what you see.

This will help you understand
A bubblemix recipe
I got this from Justin McGuire on the ABC Science Teaching list: A recipe for bubble mixture:
3 parts concentrated detergent (Morning Fresh or Dawn work well)
7 parts warm water
1 part sugar or glycerol (it helps the bubbles to last longer)

Mix the ingredients very thoroughly.

A few tips
Bubble mix keeps well in an airtight container. It works better if it is at least two weeks old. I once used a single 20L batch in science shows for over a year and it kept getting better.

Hard water isn't very good for bubble mixture.

Vinegar can help clean it up.

Don't let it soak into carpet.

This will help you join the Teaching Science list


The science behind the enquiries

The cubic bubble
The bubble surface squeezes in so as to give the maximum volume for a give surface area. If there are other constraints, like bits of wire that the bubbles stick to, this can vary the shape of the bubble. With large and multiple bubbles, there are lots of conflicting forces, but they still reach a quick balance.

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Why the spiral bubbles form
If you stop and think about it, the spiral bubble is no more surprising than the flat bubble you get in a circle of wire. Once again, the effect of surface tension is to make the surface area as small as possible, stretched between the boundaries. Since the outer wire is spiral, the bubble must be spiral as well.

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Lifting with surface tension
The idea of this demonstration is to let you see how surface tension tries to reduce the surface area of even a flat film. In this case, the only way it can do this is to pull the slider up the Y, but this only happens after you have lifted the whole gadget clear of the soap solution. Can you work out why that is?

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A cylindrical bubble No help this time, just a question: if the bubble is supposed to always arrange itself to have the smallest possible surface area, why does it bow in? (The premise is true, the question is misleading :-)

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The rapid bubbles

Why does the dry ice do this? The main reason is that the gas from any solid takes up much more room than the original solid. Dry ice is solid carbon dioxide, but it does not melt to a liquid form: it sublimes - it goes straight from the solid state to the gas, without forming a liquid at the sorts of pressure we live under.

When you put the dry ice under water, it takes heat from the water and uses this to provide the heat needed to make the solid turn into a gas. The gas is still very cold, and this is why you see water vapour ("smoke") all around the place.

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String tricks
The film of soap solution is elastic, pulling in all directions. When there is film on both sides of the thread, there is no lopsided pull on the thread, but as soon as you burst one part of the film, the remaining film pulls only in one direction.

Back to the details | Back to the index Joining Teaching Science
The ABC Teaching Science list may be accessed through this link http://www.abc.net.au/science/io/faqts.htm. It is a list for people with an interest in teaching science

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This file is http://members.ozemail.com.au/~macinnis/scifun/bubbles.htm, first created on August 19, 1997. Last recorded revision (well I get lazy and forget sometimes!) was on March 21, 2003, when I added the bubble mix recipe.

Worried about copyright? You need to go look at my fine print. Well, maybe you don't after you read the next paragraph, but do it anyhow . . .


©The author of this work is Peter Macinnis -- macinnis@ozemail.com.au, who asserts his sole right to the product as it is packaged here, recognising that many of the ideas are common. Any non-profit educational or home use is completely acceptable without let or hindrance. Copies of this whole file or site may be made and stored or printed for personal or educational use.
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