You might have seen my recent post on walking rainbows. It is an introduction for children to see how water can move from one place to another defying gravity using capillary action. I wanted to build on the concept of capillary action and show the kids how it is relevant in their everyday world.
There’s nothing more everyday at our place than the outdoors. We are lucky to live in Sydney where the weather really is conducive to being outdoors for most of the year.
The logical choice for me was to show how plants use capillary action to move water (and some nutrients from their roots to leaves and petals).
Most plants get their water via the ground. Plants therefore need a system to get the water from the ground and distribute it to the various parts above the ground that require the water. Plants do this using capillary action (for another simple experiment on capillary action head to our walking rainbows).
What you need:
- Glass or jar with the label removed
- Food colours (I like the Queen brand that come in individual bottles)
- Eye dropper or syringeWater
- White flower(s). We used carnations but you could also use white gerberas or daisies.
- Paring knife or scissors
- Measure a half cup of water and pour it into a glass or jar. You may like to set up multiple glasses for a multi-coloured array of flowers.
- Add 5 to 6 drops of food colour to the water in the glass.
- Trim the stems of the flowers at a 45° angle. A shorter stem will also yield faster results.
- Place the flowers in the water
Ask your child what they think is going to happen to the flower/s and see if they can give you a reason for their thinking.
If you have done the walking rainbows experiment, it would be interesting to see if they make any link between the two. If you haven’t done it, you might want to do that one next.
Hint – the first changes do not happen for several hours. When I did this activity with my kids, we set it up just before bed time so that they did not lose interest before they got the first signs of change.
|Day 1||Day 2||Day 3|
Pre-school to early school years
Explain that the flower stems draw up water and deliver the water to all of the parts of the plant that need it, including the leaves and petals.
Water evaporates from the flowers and then more water travels through the stem to take its place. In nature, if there is not enough water in the soil to replace water that evaporates, the plants become dry and wilt and will eventually die.
Years 2 to 3
If you haven’t already done the walking rainbows experiment, start with a discussion about gravity and ask the child or children if water normally travels up out of a glass or jar if you put something like a straw in it. Most kids will answer “no”. You could talk about the reason for that, which is that in normal circumstances gravity is keeping the water in place in the absence of any forces acting against it.
Now you can introduce the concept of capillary action. Capillary action occurs where a liquid such as water travels upwards in very narrow tubes (the narrower the more effective) and will defy gravity!
If you have done the walking rainbows, then this is an opportunity to ask if they know how the water can travel through the stems against gravity. Relate the discussion back to the way that the water travelled through the paper towels and see if your child can transfer their learning.
Years 4 to 6
For years 4 to 6, you can start with the same discussion as for years 2 and 3. If the children are interested then you can provide a further explanation about the way that capillary action works.
The water drawn up into leaves and petals of a plant undergoes a process called transpiration, which is when it evaporates. In this experiment the dye that travelled in the water doesn't evaporate, and stays around to colour the flower.
The loss of water generates low water pressure in the leaves and petals, causing more coloured water to be pulled through the stem.
The water travels because of capillary action. Capillary action occurs when water travels up through a thin tube. It travels against gravity because of a combination of the forces that keep the elements that make the water connected (cohesion) and the connection of the water to the sides of the tube (adhesion) and the surface tension of the water. The combination of these forces allows the water to travel up. The thinner the tube, the stronger the force.
If you and your kids liked this experiment then you'll love our Chemistry-in-Action kit!