We were all told as children by our mothers not to play with our food. But there is a fascination about some of the gooey fluids we consume.
If you pick up a spoonful of rather thick honey and turn it upside down, it takes several seconds before it starts to fall, but then it falls quickly. In my talk I shall demonstrate this phenomenon, and show a video of a computer simulation, using a finite element program. This computer program has also been used for some similar industrial flows; e.g. for molten glass slumping into a mould.
Everyone studying mathematics to Year 12 level learns about exponential growth. Indeed the word `exponential' has become almost a popular equivalent of `extremely rapid' when talking about growth. Whenever a rate of increase in the size of something is proportional to its present size, the growth is exponential. The size increases for ever as time increases forever.
Growth can be much more rapid than exponential. For example, if the rate of increase is proportional to the square of the present size, the size explodes at a finite time. This is easy to show using Year 12 calculus.
An `explosion' of this nature happens to the hanging length of the honey. There is a finite point of time, which can be predicted from the size of the spoonful and the viscosity of the honey, at which this length suddenly increases. You don't have to wait an infinite amount of time to get the honey onto your toast.
This electronic document has been modified
from that constructed by
Ross Moore
for the
National Symposium in Mathematics, UNSW, 23 February 1996.
Thu Jan 30 1997