Materials:

1 metre of 8mm x 8mm hardwood
Plastic propeller (100 – 200mm across)
Bead, paper clip, 300mm of 4mm dowel
4x wheels, elastic band, cereal packet
(Cardboard axle supports?)
Wood glue, scissors, sandpaper
Small saw, drill and small bit
Pliers
(All of the above are available from educational
suppliers e.g. KCS)

By using cardboard triangles (from cereal packets) to support the corners, there is no need to make difficult wood joints. The cardboard will hold the pieces in place, even if the ends are not cut very square.

Make the base rectangle first, followed by the uprights and the cross piece to hold the propeller system. Note that the front upright needs a small hole drilled about 8mm below the top. This is to hold the axle for the propeller.

Attach the axle supports, suitable axles (150mm of dowel) and the push-fit wheels. Finally, position the propeller, bead, elastic band and paper clip. The paper clip is straightened out to make the axle for the propeller. One end is bent into a hook to hold the elastic band. The other end is passed through the hole in the front upright, through a bead and then through the propeller. Finally, the end is bent over to engage the side of the propeller, so that when the paper clip turns it will turn the propeller with it.

Make a marble maze by sticking strips of wood on to thick card. You can then use a magnet under the card to guide a ball-bearing through the maze.

The diagram shows a very simple arrangement. Perhaps you could make something more difficult. How long does it take to move your ball-bearing through your maze. Can your friends do it any more quickly?

You need a fair test for the powders or liquids. The point is that we want to test the powders, so everything else must be kept the same in the tests. This would include:

The same - amount of water, temperature of water, time of washing, amount of stirring, amount of washing powder,
type of dirt and stain, size and type of linen.

Stain your cloth samples. A good idea is to put several stains on each piece of cloth. Only a small drop it needed in each case so a match stick dipped in the stain is a good dispenser. Try not to flood the cloths. Remember that the washing machine is in miniature, so the stains need to be in miniature as well.

Provide standard hot water. This might be available from a hot tap that has been run for a while. Otherwise, boil a kettle of water. Otherwise decide how much water you want in your mug. Put in a fixed amount of cold water and ask an adult to top it up with boiling water. That should provide much the same final temperature each time (Well, it's a reasonable attempt anyway).

Remember to rinse the samples after washing. Give each detergent a mark out of 5, say:

5 = excellent, totally clean
4 = good, nearly all stain gone
3 = moderate, some stains removed
2= poor, few stains removed
1= awful, little improvement

Apart from testing different powders or liquids, you could compare the performance of a single detergent using water at different temperatures. Some families have changed washing powders as a result of these tests!

The rough idea is to make a miniature washing machine using a mug of hot water with a teaspoon of washing powder. A small piece of linen can be stained or made dirty and then it can be washed by stirring it in the 'washing machine' for a fixed time (5 or 10 minutes). It should then be possible to compare the effectiveness of different washing powders or liquids.

Modern detergents are very effective so the stain will need to be resistant to cleaning. The comparisons will not be very useful if every piece of linen emerges pure white from the wash, so we need a real challenge. Dried-in stains are harder to clean than wet ones so whatever stains you use (beetroot, coffee, tea, etc.) dry them thoroughly. A hair dryer might be useful if you want to do this quickly for one or two samples, otherwise hang the samples on a central heating radiator (Do not hang them on an electric heater). It is good to have one stain that will be almost impossible to remove with detergents. Something based on grease or old engine oil fits the bill very well, but you will not want too much of it around for fear of staining clothing.