What it shows
A wind vane turns until its large tail is pushed downwind, so the small arrow head points into the wind. Winds are named by the direction they come from, and the direction often changes before the weather does.
The science
Wind pushes on both ends of the vane, but the tail has a much bigger area than the head, so it receives a bigger force and swings away downwind. The vane settles when the two sides are balanced, which happens only when the arrow lies along the wind. Because the pivot is at the balance point, even a light breeze can turn it.
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 plastic bottle with sand in it as the base
- A pencil with an eraser
- A pin
- A straw
- Stiff card for the arrow head and a larger tail
- A card compass rose marked N, E, S, W
- A magnetic compass or a phone compass app to set north
Safety
For this project: An adult should push the pin through the straw into the eraser.
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.
Cut a small triangle for the arrow head and a bigger one for the tail from the card.
Slit each end of the straw and push the triangles in, head at one end and tail at the other.
Balance the straw on a finger to find its middle, and push the pin through that point into the pencil eraser.
Push the pencil into the sand-filled bottle so it stands upright.
Lay the compass rose flat under the vane and turn it until the N mark faces true north by the compass.
Blow gently from one side and check that the head swings to face you.
Place the vane in an open spot away from walls and read the direction twice a day for a week.
Write each reading as "wind from the west" and note the weather that followed.
What you should see
A table of wind directions for a week. In most Indian towns the monsoon wind comes steadily from one quarter, and a change in direction often arrives with a change in weather.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Which way does the arrow point?
Into the wind, towards where the wind is coming from.
2Why is the tail bigger than the head?
The bigger area catches more wind and gets pushed downwind, turning the head into the wind.
3What is a westerly wind?
A wind blowing from the west towards the east.
4From which direction does the south-west monsoon reach most of India?
From the south-west, off the Arabian Sea and the Bay of Bengal.
Take it further
Add a small anemometer beside it and record wind speed with direction.
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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