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National STEM Learning Centre

Skip to 0 minutes and 8 secondsSPEAKER: This is a really lovely activity to do with your children to practise the states of matter and practise the parts of the water cycle where the children can see it demonstrated within the classroom. It's a really simple activity. You just need a nice plastic bag that you just got from a supermarket there, some water, and we use some blue food colouring, just so it's easy for the children to see the colour of the water in the bag. The first thing I would ask the children to do was to draw out the different stages of the water cycle. So we're thinking about the rain, cloud formation, and the evaporation from the sun. So I'd get them to draw it.

Skip to 0 minutes and 44 secondsSo I've just got here a permanent marker, and onto the side of the bag, I would just draw those different things. So the first thing would be nice cloud to show where the water has condensed into the sky, a river, or a sea, or something down the bottom, a nice lake, and the sun up in the top corner. Then I would ask the children if they could think about the words, the vocabulary that they would need to represent the different parts of the water cycle. Hopefully, they'll have practised this in class. If you're not sure, you could maybe present those words for them and ask them to place them where they are on their diagram.

Skip to 1 minute and 21 secondsSo obviously, we've got evaporation from the sea, from the lake, up into the sky. So I just draw that with an arrow to show that that's where it's going. So the water is evaporating off the sea up into the air. I might draw some rays coming out of the sun. I know the sun doesn't have rays, but you know just to visually represent that. And then the next stage would be the water droplets, the vapour that has evaporated from the sea, condensing into the cloud. So I might draw an arrow across to the cloud. And the final part of our water cycle would be the rain falling down as precipitation.

Skip to 2 minutes and 2 secondsThe final part of the drawing there would be to ask the children to write on the words. So we'd have evaporation, condensation in the clouds, and precipitation down there to show where the rain is falling. Then get to the fun bit. So the children can add some water to their bag.

Skip to 2 minutes and 21 secondsAnd we've just got some blue food colouring. Felt pen colouring works fine, anything that will just give it a bit of a tint so the children will be able to see that demonstrated. So add that to the bag. Seal it up, which is why freezer bags are really good because they make a brilliant seal. Give it a bit of a mix to make that nice blue liquid, and there we've got a finished article. This then needs to be taped to the window of the classroom.

Skip to 2 minutes and 49 secondsWhen it's taped there, hopefully what will happen in a warm classroom is that water will evaporate from the bottom here, evaporate up the bag as water vapour, and then condense onto the outside of the bag as it gets cooler. And the children will see that condensation on the bag. And then when you tap it, you get rainfall coming down, and the entirety of the water cycle is represented.

Water cycle in a bag

In this video, Karen creates a model of the water cycle in a freezer bag.

She first draws a simple diagram of the water cycle on the outside of the bag. Then some water is added to the bottom of the bag with a little blue food colouring so that it can be seen. When the bag is stuck onto a sunny window, the water evaporates, and then condenses higher up, and drips back down again, modelling the water cycle.

Describe

In the comments below explain what is happening inside the bag after the bag warms up. What misconceptions might this activity address?