What it shows
A vertical-axis wind turbine spins whichever way the wind blows. The curved half-bottle blades catch more push on the open side than the round side, so the rotor keeps turning.
The science
Wind pushes harder on the hollow side of a half-cylinder than on the rounded back, because the open face traps the air while the round back lets it slide around. The difference in push gives a turning force around the axle. Since the shape works from any direction, no tail or turning mechanism is needed.
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.
- One 1 litre plastic bottle
- Two round cardboard discs 12 cm wide
- A bamboo skewer or thin dowel as the axle
- A bottle cap or small bead for the bearing
- Strong tape and glue
- A battery or USB fan for testing, or a steady breeze outdoors
Safety
For this project: An adult must cut the bottle and the skewer ends. Keep fingers and hair away from the spinning blades and from the fan guard.
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.
An adult cuts a straight 12 cm length from the middle of the bottle and splits it along its length to make two half-cylinder blades.
Mark the centre of each disc and push the skewer through both, 12 cm apart.
Tape the two half-bottles between the discs, one facing left and the other facing right so they overlap in an S shape.
Fix a bead under the lower disc to cut friction on the base.
Stand the turbine on a plastic lid with a small dimple for the skewer to sit in, and let the top of the skewer pass loosely through a hole in a card holder so it stays upright.
Place it about 50 cm from the fan on low speed and watch it start to spin.
Count the turns in thirty seconds at low, medium and high fan speeds.
Record your counts in a table and plot them.
What you should see
The rotor spins in a steady direction whichever side the fan blows from, and spins faster as the fan speed increases.
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 a vertical axis turbine?
One whose axle stands upright, so wind from any side turns it.
02Why an S shape?
It lets air flow from one blade into the other to keep pushing.
03How could the rotor drive a generator?
By connecting its axle to a small dynamo or motor.
04Where is wind energy used in India?
Large wind farms in Tamil Nadu, Gujarat and Rajasthan.
Take it further
Add a small DC motor on the axle and measure its voltage at each fan speed, or light a red LED with a 330 Ω resistor in series.
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
Science projects
Physics Working Models Explained
Twenty classic models, how each works and how to make it
Find out more about physics
Free, well-known places to explore the subject further. Ask a grown-up before you sign up for anything or type your name anywhere.