Bin-bag hot air balloon
A big, very light bin bag filled with hot air from a hairdryer that floats up to the ceiling.
Age : age 5+ as active spectators; the grown-up holds the hairdryer
Materials
- A very thin, large bin bag (about 90 L) : As light as possible: thick bags won't take off.
- A hairdryer : Hot setting, high speed.
- Tape : To seal any holes.
- A few paper clips : A little weight at the bottom keeps it steady.
- A draught-free room with a high ceiling : Or outdoors on a very still day.
Steps
Lift-off
- Check the bag has no holes, and tape any you find.
- Clip two or three paper clips around the opening.
- One child holds the top of the bag, opening facing down; another holds the opening wide.
- The grown-up blows hot air into the opening, without touching the plastic with the nozzle.
- Heat for 1 to 2 minutes, until the bag is full and pulls upwards.
- Switch off the hairdryer, count to three and let go all together.
Hot air takes up more room than cold air for the same weight. So the bag full of hot air is lighter than the air around it, and it rises. As the air cools it shrinks and the bag comes down: that's how real hot air balloons work.
Going further: time the flight with 1, 2, then 3 paper clips and compare.
If it goes wrong
- Won't take off : Thinner bag, heat for longer, remove a paper clip.
- Flips over in the air : Add a paper clip on each side of the opening.
- Drops straight away : Tape the holes, close doors and windows.
Safety
- No candle or flame under the bag: plastic melts and catches fire. The hairdryer version is enough.
- A plastic bag never goes over anyone's head: suffocation risk, remind the children.
- The hairdryer nozzle gets hot: the grown-up holds it.