Saucer of milk
2 or 3 different food colourings
Cocktail stick
Washing-up liquid
What to do ...
Leave the saucer of milk out on a kitchen worktop for a couple of hours, until it reaches room temperature.
Pour a couple of drops of each food colouring in different places in the saucer.
Put the end of the cocktail stick in a bit of washing-up liquid.
Put the cocktail stick in the centre of the milk and watch what happens.
You will notice ...
The colours race to the sides of the saucer and you see swirling patterns of colour in the milk.
Why?
Surface tension holds a drip (or blob) of liquid together. It acts like skin, holding the liquid in place.
Soap rips surface tension apart so when the washing-up liquid touches the milk the surface tension at that point breaks and the colours rush to the sides of the saucer where the surface tension in the milk is as strong as ever.
Try this ...
Dip the stick in the centre of a blob of colour this time.
