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Bubble Trouble

 
 

Overview

The science

A water molecule is made up of hydrogen and oxygen atoms that are attracted to each other. This attraction also causes surface tension, an attractive force that occurs on the surface of liquids. This means that if you try and blow a bubble using just water it will not work. When soap molecules (washing-up liquid) are added to water they reduce the surface tension and enable you to blow bubbles.

Bubbles will always try to form a sphere. Spheres have the smallest surface area for the volume of air inside so it takes the less energy to form this shape compared to other shapes.

Materials, per group

  • 500 ml of bubble mixture, made to the Science Museum recipe below 
  • Spoons
  • Hand whisk

Give your students pre-made bubble-blowers or allow them to make their own using the 'Making Bubble Blowers' activity sheet using the following materials:

  • Bowls and plates made of expanded polystyrene or other plastic
  • Coat hangers
  • Paperclips
  • String
  • Scissors

Teachers’ materials

  • Metre ruler or tape measure
  • Camera (optional)
  • Classroom assistants or parent helpers (this activity is quite messy, so the more people you have to help the better)

Science Museum bubble recipe

  • 1/2 mug of washing-up liquid
  • 3/4 bucket or tub of warm water 
  • 1 mug glycerol (available from chemists) 

Add the glycerol to the water and stir slowly while gradually adding the washing up liquid.

Bubble mix is dependent on the environment and temperature so you may have to experiment to find the best mix.

  

Running the investigation

Before you start:

  • Protect tables with plastic washable tablecloths, newspaper or dustbin liners that have been cut open.
  • Have all the equipment in place on the tables.
  • Make the bubble mixture and leave it to stand in a warm place for a couple of hours – the longer it has to settle, the better it becomes. 

With your pupils:

  • Ask each group to define 'best bubble' and how it can be tested or measured. For example, if making foam it might be the tallest peak you can make; if blowing bubbles it might be the largest size or the one that lasts longest.
  • Discuss as a class what characteristics make the 'best' bubble – is it the largest, the longest lasting, the tallest foam…? Introduce the idea that people have different views on what is 'best'.
  • Set the challenge to make the best bubble allowing free investigation with the equipment provided. Refer to the images in the 'Making Bubble Blowers' activity sheet for inspiration if necessary. We recommend you allow about 45 minutes but you can shorten or lengthen this.
  • Get pupils to make and try different bubble-blowers, recording the implements used, their techniques and their results. Recording can be in the form of measurements, photographs or sketches. For a shorter investigation, provide a selection of ready-made devices, e.g. a coat hanger wrapped in string.
  • Allow time for each group to demonstrate what they have come up with and present their findings about what makes the best bubble.

Practicalities

  • This investigation is messy! Have cleaning materials available including absorbent cloths, towels and aprons. Allow time in your planning for washing hands at the end.
  • Using glycerine in your bubble mix will help the bubbles to last longer and be stronger. Don’t add too much or the bubbles will become too heavy.
  • Bubble mix is dependent on temperature, humidity, etc., so we recommend you make and test your bubble mix in advance to ensure that it works, even if you have followed a recipe.
  • On hot days mist the air with a plant spray to help the bubbles last longer. In winter place a couple of bowls of water near radiators for an hour before you start the activity.
  • Although it's tempting to run messy activities like this outside, bubbles don’t like dry air or too much wind. For the same reason avoid air conditioned rooms where possible.

Discussion

This activity provides great scope for discussing concepts such as predicting and testing, in a visual, fun way. It is also useful for introducing the idea that not everyone agrees on what is 'best' or 'better' and that different views can be equally valid.

  • What is the best bubble?
  • Does everyone agree on what the best bubble is? If not, why not?
  • Which blower makes the best bubble?
  • Which mixture makes this bubble the best?
  • Can you make bubbles from just water?
  • Do you think you could make the bubbles even better? How?
  • Did you change anything that you were doing along the way? Why?
  • Do you think there are other ingredients that you would want to try?
  • What else could you use to blow a bubble?

Extensions and adaptations

  • Rather than running an open-ended investigation, you might set a competition by defining the challenge yourself e.g. make the largest bubble, the bubble that lasts the longest or the strongest foam that can hold a polystyrene bowl with five marbles in it. Groups compete to complete the challenge.
  • Provide three different types of pre-made bubble mix to investigate, making deductions about the proporations of teh ingredients used in each. 
  • Add paint to your bubble mix and use a straw to blow bubbles onto paper. This is a good way to record the size of the bubbles.
  • Compare bubbles with other things that float in the air (e.g. seeds or feathers) - what are the similarities and differences?

Links to everyday life

Bubbles are formed because the ingredients in soap and washing-up liquid reduce the surface tension of the water. The same ingredients also loosen dirt and grease to help get people and plates clean. As the ingredients in the soap become used up by the dirt and grease the bubbles disappear.

Bubbles form better in warm water than cold water. You can experiments with this when you are adding bubble bath to running water.

Bath time

Bubbles also have a very practical use in your toolbox. A spirit level is a glass tube filled with ethanol and a single bubble. It indicates that a surface is level when the bubble is positioned exactly between two lines on the tube.