What it shows
Water climbs up through the tiny gaps between soil grains. Fine clay lifts water highest but slowly, and coarse sand lifts it only a little but fast, which matters for how crops reach water.
The science
Water molecules stick to soil grains (adhesion) and to each other (cohesion), so water is pulled up narrow gaps against gravity. The narrower the gaps, the higher the water can rise, but friction makes it slower. Sand has wide gaps, clay has very narrow gaps.
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 clear plastic bottles or tubes, 20 cm long, with the bottoms cut off
- Muslin cloth and rubber bands
- Dry sand, silt or fine garden soil, and clay soil
- A shallow tray of coloured water
- A ruler and a stopwatch
- A funnel to pack soil evenly
Safety
For this project: An adult must cut the bottles. Wash hands after handling soil and wear a dust mask when pouring dry clay.
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.
All the safety rulesStep 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.
Tie muslin over the cut end of each tube with a rubber band.
Fill each tube to the same height with dry sand, silt or clay, tapping gently to pack evenly.
Stand the tubes upright in a tray with 1 cm of coloured water.
Start the stopwatch and mark the water front on the tube every minute.
Record the height of the colour front against time for each soil for the first 20 minutes.
Leave the tubes for a day and measure the final height reached.
Plot height against time for the three soils on one graph.
Note which soil rises fastest and which reaches the greatest height.
What you should see
Sand rises fast but only a few centimetres, while clay rises slowly to a greater height. The graph shows the trade-off between speed and height.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is capillary action?
The rise of liquid in narrow gaps against gravity.
2Why does clay lift water higher?
Its gaps between grains are narrower.
3Why does it matter to farming?
It decides how much water plant roots can draw from below.
4Why pack the soil evenly?
Uneven packing changes the gap size.
Take it further
Mix sand and clay in different ratios to find the mix that gives good height and speed.
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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