Milk in Motion PDF Print E-mail

Get ready milky mesmerisation with these seriously groovy psychedelic patterns.

 

You will need:


• milk (full cream)
• saucer
• several colours of food colouring
• dishwashing detergent
• Toothpick or pencil

 

What to do

1. If you can, do this activity in a sink, so cleaning up is easier.
2. Place some milk in the saucer.
3. Gently drip four separate drops of food colouring on the milk. Space the drops out evenly. Use different colours if you can.

4. Watch the milk and colouring for a while. Does anything happen?
5. Smear some detergent on the tip of the toothpick and touch the toothpick to the centre of the milk.
6. You should find the colours jump away from the toothpick. They may start to swirl around and mix together.

 7. Try touching the toothpick against a few other spots on the surface of the milk.

 

What's happening?


The milk moves when the detergent reduces the milk’s surface tension. As it moves, it drags the colouring with it, producing the swirling effect. One way to describe surface tension is to think of the surface of the liquid like a stretched-out balloon skin. Every point on the surface of the liquid is under tension.

Without detergent, everything is stretched evenly, so nothing moves on the surface of the milk. As soon as you add detergent to the milk, the surface tension at that spot is reduced meaning the surface is no longer stretched evenly. This makes the milk start swirling.

At the same time, detergent reacts with proteins and fat in the milk (that’s why detergent is good for cleaning greasy plates), causing even more movement.

 

© CSIRO

Article generously contributed by CSIRO

Check out other activities for Kids by CSIRO:

Last Updated ( Saturday, 12 January 2008 )
 
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