rAs Kids⬆️lift ⬇️weight ➡️thrust ⬅️drag
🎒 What you need
- a length of elastic or rubber bands, string, and a bag or tin
- stones as known weights, and a ruler or marked stick
- a piece of cardboard and a flat open area
✋ Do this
- Make a scale: hang the elastic from a branch, attach a tin, add stones one at a time and mark the stretch each time. You now have a force meter in units of stones.
- Weigh a cardboard sheet with it. That is weight, and it never changes direction — always straight down toward the Earth's centre.
- Now hold the cardboard flat and run, then hold it edge-on and run. Same object, hugely different push. That difference is drag, and it depends on the area facing the airflow.
- Tie the cardboard to the elastic and pull it through the air at a steady speed. Read the stretch. You have measured drag as a number.
- Repeat at double the speed. Note that the stretch grows much more than double — drag rises far faster than speed does. That single fact governs the range of every aircraft.
- Draw all four force arrows on your cardboard, sized to your measurements. Then state the hover condition in one line: lift equals weight, thrust equals drag.
💡 Why it works
A hovering drone is not doing nothing; it is holding lift exactly equal to weight while burning battery. Because drag climbs steeply with speed, flying fast is disproportionately expensive, which is why delivery drones cruise at an efficient speed rather than a maximum one. Every payload gram you add must be paid for in lift, and lift is paid for in battery.
🔥 Challenge
Build two cardboard shapes with identical weight but very different drag. Measure both, then predict which would fly further on the same battery and justify it with your numbers.
📖 New words
liftthe upward force generated by pushing air downward
dragthe resistance of air against a moving body, rising steeply with speed
payloadthe useful weight carried, such as a camera or medical supplies
📐
Force Measurer
Tap when you have finished this module.