Grow a Rainbow!

This experiment is showing ‘capillary action’

Published in
2 min readApr 7, 2020


The second STEM challenge as part of our ongoing partnership with Outdoor Ted, an organisation that helps primary schools in our local communities to get a varied outdoor education. This is part of their new initiative, ‘Indoor Ted’, aimed at inspiring children and families to take on fun and educational tasks at home during this unprecedented time. This week we present ‘grow a rainbow’, we look forward to seeing your creations on social!

You will need:

· Kitchen roll/paper towel

· Felt tip pens

· Two small tubs/bowls of water

· Paper clip

· Thread


· Cut your kitchen towel into the shape of a rainbow.

· Use felt tip pens (not permanent markers) to colour a rainbow about 2cm up on each end of your rainbow.

· Attach a paper clip to the top of your rainbow and tie some thread to it. This will give you something to hold on to.

· Pour some water into your two tubs.

· Hold your rainbow so both ends are submerged into the water.

Tip — if you don’t want to hold your rainbow, attach your paper clip to a glass to support your rainbow.

Watch your rainbow grow!

The Science behind it!

This experiment is showing ‘capillary action’!

The water molecules like to stick to things — this is called adhesion. They also like to stick to themselves — this is called cohesion. In your rainbow the water is being ‘sucked’ through the holes in the paper towel because of adhesion and the rest of the water molecules follow due to cohesion. Eventually the water pressure will slow down and the pressure of gravity means your rainbow will stop moving!



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