This game is a good model for children to understand the ‘runaway’ exponential effect of chain reactions. The principle behind nuclear reactors.
Children pair up with each other as in Elbow Tag, holding hands or linked arm in arm, and scatter around the playing field/area. One child is chosen to be IT (the chaser). When a pair is caught they split up and each of them also become chasers. The game ends when there are no pairs left.
Those in pairs will find that by being arm in arm or holding hands they generally cannot run as fast and behave a bit like slower larger molecules. When chaser catches a pair this represents a small molecule striking a slower one causes it to split and in this case produce two more fast-moving molecules. Although the game is slow to start with because each time two more players become chasers very soon there are no more pairs left.
It’s not a perfect model because this is not done randomly as it would happen in reality, but it’s a useful quick game to show the exponential effect that takes place in chain reactions.
This game could even be taken a step further if you wished to demonstrate the controlled chain reactions that go inside nuclear reactors, by introducing a new element ‘the control rods’.
Give some players coloured bands to identify them from other players as ‘control rods’. Control rods have to catch the fast moving individuals. Once caught an individual can no longer chase pairs but has to find another fast moving individual (who may or may not have been caught by a “control” player), join up with them and become a slower moving pair. Hopefully, if you play with large enough numbers, you’ll reach a stage in the game where you reach a controlled balance of players breaking pairs apart and other recombining them. Similar to reactors you may find it useful to experiment using different numbers of “control” players so that you could keep the game going ad infinitumby