What it shows
You compare tissue papers or paper towels for absorbency and cost by measuring grams of water held per sheet and per rupee. It is a practice in fair testing, averaging and unit costs.
The science
Paper is made of cellulose fibres with many small gaps between them. Water climbs into these gaps by capillary action and sticks to the fibres. A towel with more fibres and more gaps holds more water, but it is also heavier and may cost more, so the best buy depends on grams of water per rupee.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Three or four brands of paper towel or tissue
- A kitchen scale (to 1 g, or 0.1 g if you can borrow one)
- A bowl of water and a measuring cup
- A clip or tongs
- A calculator
- A notebook
- A pencil
Safety
For this project: Wipe up the water so the floor is not slippery. Use clean tissue only.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Cut one sheet of each brand to the same size, say 20 cm by 20 cm, big enough for a kitchen scale to show the difference.
Weigh each dry sheet and note the weight.
Dip each sheet in water for ten seconds and hold it up for ten seconds to drip.
Weigh the wet sheet and subtract to find the water held.
Repeat three times for each brand and calculate the average.
Find the cost of one cut piece from the pack price, the sheet count and the share of a sheet that you cut.
Divide the water held by the cost to rank the brands as best value.
Present a table and a bar chart showing the winner.
What you should see
Thicker towels hold the most water per sheet, but a cheaper brand may give the best water per rupee. The table gives both rankings.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What is capillary action?
Water rising through narrow gaps.
02Why repeat three times?
To reduce errors and find an average.
03What does best buy mean here?
The most water held for each rupee.
04Why use equal-sized sheets?
Otherwise the test is not fair.
Take it further
Test the strength when wet by hanging coins on each sheet until it tears.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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