You need a jug of water, a roll of kitchen towels and some blue food colouring or ink for this activity.

First make the water deeply coloured, so you can easily see what is happening.

Now pour a small amount of water – just a few drops – onto the centre of a square of kitchen towel and notice what is happening.

Look closely and if possible, take digital camera pictures (from exactly the same place) every 30 seconds.

Then print the pictures and put them side by side on a wall board. Write a description of what they show.