Making rain

With all the rain lately kid M has been asking ‘why do the clouds drop rain?’. So I thought we’d do this little experiment that shows how the rain cycle works. It’s not a super hands on one for the kids (especially as it involves boiling water) but there are bits they can help with and it is a good one for watching to see what happens (which can easily be done at a safe distance from the boiling water!).

What you need:

  • Glass jam jar (essential – two if you want to do both at the same time like we did. Wide jars work best apparently but our Bonne Maman ones worked just fine)
  • Hot water (essential – obviously please be careful with this)
  • Foil (essential)
  • Ice cubes (essential – although we didn’t have any ice cubes so improvised with a pot of frozen apple mush. You could use anything frozen that fit nicely on the top of the foil).
  • Plastic cup (essential – ideally see through. We used a room temperature glass cup for this and it worked fine).

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What to do:

  • Pour the hot water (recently boiled) into the jam jars until they are about half full.
  • Pop the plastic cup over one of the jam jars.
  • Cover the other jam jar with the foil.
  • After 1 minute put the ice cubes on top of the foil.
  • Watch the jars and have a look inside the plastic cup after a few minutes.

Tips/extra bits:

  • The two jars are basically showing the same part of the water cycle, but it’s nice to do them together so the kids can see the rain in one and then have a closer look/touch the water droplets in the other as both jam jars get quite ‘cloudy’ with condensation.
  • The glass we used to put over the jam jar was wider at the top than the jam jar and so we created rain on the outside as well as the inside. This actually was a bit more fun for M as she could see it clearly dropping from the sides.

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The science bit

In both jam jars the hot water turns into vapour and rises (evaporation). The vapour cools either as a result of the cold foil (jam jar 1) or by rising (jam jar 2). When it cools the vapour turns back to water droplets, and hey presto rain. The water droplets formed on the inside of the plastic/glass cup as a result of the vapour rising and cooling are condensation.

Explaining it to children

When water gets warm it turns into water vapour, which is water in the air that you cannot see. This vapour rises up with warm air. When it rises up it cools down and goes back to being drops of water again. Small drops of water join together to make a cloud. Inside the cloud more of these water droplets can join together. However when they get too heavy they fall from the cloud as rain. Inside the jam jars drops of water collect at the top when they have cooled down. These drops can also join together and fall down like rain when they are too heavy.

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Experiment based on an activity from the fantastic Usborne Activities: 365 Science Activities book.

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