⚙️🔃 ⬇️ ⚖️ 🪨🪨

A motor with a paper propeller on one end of a balanced stick, with stones piled on the other end.

🎒 What you need

a small DC motor from a broken toy or fan, plus AA batteries and wire
stiff paper or a plastic bottle to cut a small propeller, and a small cap to fix it to the shaft
a straight stick, a stone to balance it on, string, and small stones as weights — with an adult supervising

✋ Do this

SAFETY: spinning blades hurt. Keep fingers, faces and little brothers away. Use paper or thin plastic blades only, never metal. Wear something over your eyes if you can, and never lean over it.
Cut a small two-bladed propeller and twist each blade the same amount in opposite directions — like your paper spinner in module 2. Fix it to the motor shaft.
Balance your stick across a stone like a see-saw. Tape the motor at one end, pointing so it blows DOWNWARDS.
Run the motor. Watch that end of the stick lift. That lift is thrust and you are looking straight at it.
Now add small stones to the other end until the stick balances level. Those stones weigh the same as your thrust — you have just measured a force.
Change one thing: flatter blades, more twist, or a fresh battery. Measure again in stones. Write both numbers down side by side.

💡 Why it works

Drone engineers do exactly this on a proper test stand, using grams instead of stones, because a drone can only fly if its total thrust beats its total weight. That is why every extra gram — a bigger battery, a heavier camera — costs flying time. You have now measured the same trade-off with a stick and a pile of stones.

🔥 Challenge

Find the blade twist that gives the most thrust. Test three different twists, record the stones for each, and be honest if your favourite design loses.

📖 New words

thrustthe push a propeller makes

forcea push or pull you can measure

⚖️

Thrust Tester

Tap when you have finished this module.