Q1.
Now, you can hold the firki in your hand and run. You can also blow air on it. What do you observe? Does the firki rotate?
Answer
Yes — the firki rotates every time air pushes against its blades.
| What you do | What you observe |
|---|---|
| Hold the firki still in still air | It does not turn |
| Blow air on it | It turns; blow harder and it turns faster |
| Hold it up and run | It spins fast on its own |
| Move it back and forth | It rotates each time it is moved |
| Stand still on a windy day | It keeps rotating without you doing anything |
Why it turns: the blades of a firki are folded, so each blade is slanted. Air striking a slanted blade gives it a sideways push. All four blades are pushed the same way round, so the whole firki spins on its pin. When you run, you move through still air — which is the same as air moving past you.
Tip: Use a square of stiff, thin paper 15 cm × 15 cm and do not push the all-pin too tight into the stick. If the pin is tight, the firki will not spin however hard you blow.