Beatrice Lee of Moa Flat asks :-

How does glue stick stick things together?

Peter McElroy, a chemical engineer at the University of Canterbury, responded.

Most glues have to be able to wet the material to be glued. Jam or honey are like that and work as a poor sort of glue.

All things are made up of different kinds of very tiny particles, which no-one can see, called molecules. The molecules in glue are very long ones which tangle up like the straw in a birds nest and make it strong.

In jam there are some quite long molecules so it works like a glue but not a very good one. In flour there are longer molecules called starch. Mixing it up with water makes it wet the thing you want to glue and when the water dries out, the long starch molecules make it quite a good glue.

All plastic things like bags or toys are made from chemicals which are very long molecules. Most other glues are made by dissolving different types of plastics in liquids - sometimes water but more often liquids like petrol. Then they work just like flour and water.