What it shows
The rate at which a drip emitter releases water depends on the height of the water above it. Measuring drops per minute at different heights shows the link between pressure and flow, which a farmer uses to design a drip line.
The science
Pressure in water increases with depth, so a higher reservoir pushes water through the same small outlet faster. In a narrow tube the flow is not exactly proportional to height, because friction and the outlet size also matter. Real drip systems use pressure-compensating emitters for even flow.
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.
- A 2 litre bottle as the reservoir
- Thin tubing 1 m long
- A hand-made emitter: IV drip set regulator, or a pinched tube with a tiny hole
- A measuring cylinder or small cup
- A stopwatch
- A metre ruler and stand
Safety
For this project: Handle needles and cut plastic with an adult. Work over a tray so that no water spills on the floor.
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.
Fix the bottle on a stand with its neck down and connect the tubing with the emitter at the end.
Mark the height of the water surface above the emitter with the ruler.
Fill the bottle and collect the water dripping in a measuring cup for five minutes.
Record the volume collected and the number of drops.
Lower the bottle by 10 cm steps and repeat the measurement each time.
Keep the bottle topped up so the level stays roughly the same during each run.
Convert the volumes to millilitres per hour.
Plot flow rate against height and describe the shape of the graph.
What you should see
Flow rate rises with the height of the reservoir, giving a smooth curve. The data tell you the height needed for a chosen drip rate.
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 pressure head?
The height of water above the outlet that gives the pressure.
2Why does a lower bottle drip slower?
Less pressure pushes the water.
3Why top up the bottle?
To keep the height steady during a reading.
4Why is drip irrigation efficient?
Water goes straight to the roots with little loss.
Take it further
Test two emitter hole sizes and plot both curves on one graph.
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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