What it shows
A kite stays up because the wind pushes on it at an angle. The forces of wind, weight and string tension balance. A longer tail steadies the kite, and a higher wind speed raises the string angle.
The science
The kite is held at an angle so the wind deflects downward, and the air pushes it upwards and backwards. These forces are balanced by the kite’s weight and the string tension. A tail adds weight and drag at the back, which keeps the nose pointing into the wind and stops spinning. A stronger wind means more force and so a steeper string angle.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A paper or plastic kite with a bamboo frame
- Cotton thread (never sharp manja) on a reel
- Strips of cloth for tails
- A protractor and a plumb line made with a thread and a nut
- A phone with a wind speed app
- A measuring tape
Safety
For this project: Never use glass-coated or metal manja thread, and stay away from roads, trees and power lines. An adult must supervise, and fly only on an open field.
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.
Build or buy a flat kite and fit it with a bridle, a short string on the front, as the maker instructs.
Take it to an open field on a breezy day and note the wind speed using the app.
Launch with a 1 m tail and let out 30 m of string, and hold steady.
Measure the string angle by sighting along the string with a protractor and a plumb line, and note the height from the angle and length.
Land and change the tail to 0.5 m and then 2 m, and repeat the flight at the same wind speed.
Record steadiness on a scale: steady, wobbly, spinning.
On days with different wind speeds, record the string angle each time.
Plot string angle against wind speed and describe the pattern.
What you should see
A table showing the steadiest flight with a medium tail, and a graph where a stronger wind gives a steeper string angle and a higher kite.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What forces act on a kite?
Weight, wind force and string tension.
2Why does the kite need a tail?
It adds drag at the back and keeps it stable.
3How can you find the kite’s height?
Height equals string length times the sine of the string angle.
4Why avoid manja?
It can cut people, birds and wires.
Take it further
Compare two kite shapes, diamond and a box kite, in the same wind.
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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