Today we went for a quick & easy but fun experiment that is a great introduction to surface tension.
All you need is:
a saucer of milk
Q tips (cotton buds)
washing up liquid
Pour a little milk into a saucer and add a few drops of food colouring.
Dip the Q-tip in washing up liquid, just a touch, you don't want to drown it :)
Have your little scientist touch the surface of the milk with the q-tip and watch how the colour "jumps away" from the tip.
You should be able to do this a couple of times with the same saucer full providing you haven't used too much washing up liquid.
Very simple but effective, fun and is a nice little introduction to learning about surface tension.
You could try dipping a dry q-tip as well to show your little ones that the addition of washing up liquid is what makes this experiment work.
Another fun alternative to this experiment is to put a spot of several food colours into the saucer and then drop a squirt of washing up liquid into the centre of the saucer & watch the colours spread quickly.
My Little People are quite young so we didn't go too much into what happens to the molecules but this is how it works:
When you introduce washing up liquid to the molecules that make up milk, it dissolves the fat molecules (just like when we use it to clean our dishes) and the surface tension is lowered. This leaves the colouring able to move around the milk much more freely.