Marvin and Milo

Explore physics the exciting way, by trying out a simple and fun experiment. This month, Walking Water Don't forget to check back next month for the next edition...

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What you need


Seven clear plastic cups

Food colouring


Paper towels




Line up the cups and fill every odd one with water. Stir various food colourings into the water-filled cups – e.g. red in the 1st and 7th, yellow in the 3rd, blue in the 5th.

Fold some paper towels to make upside-down V-shaped arches. Trim them so that they can link every cup with its neighbour, with the ends touching the bottom of the cups.

Wait for several hours. Water will end up in all of the cups and the colours will be mixed!

Results & explanation


Water overcomes gravity and rises up the arches as it is attracted to the cellulose in them and to the water already absorbed. Once the arches are saturated, the water seeps out again and mixes with coloured water from the next arch to make new colours.


Read more about capillary action on


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