This demonstration is usually conducted as an end of term filler lesson to get students thinking about how hot air rises in relation to cold air.
A teabag (the type with a string attached) is carefully emptied of its tea and the string removed. It is upturned so it resembles a box or cylinder with the open end facing the surface of the heatproof mat. A taper or match is used to set fire to the very top of the teabag. The bag will slowly burn and after a few seconds should rise into the air.
Equipment typically required (per demonstration)
The reason the teabag rises is the result of a combination of two factors. Firstly the flame causes the air inside (and around) the bag to heat up while at the same time the burning process removes mass from the bag. At the point the air is hot enough and the bag is sufficiently light enough, the bag should rise.
- Teabag (the type with a string and tag)
- Taper or matches
- Heatproof mat
This demonstration may be conducted out of doors, however, even a very small amount of wind may disrupt the heating of the bag and it may not rise.