From 13th till 22nd March 2015, it is British Science Week, which is a great excuse for you and the kids to have a go at this simple and fun science craft.

It’s quick to set up but you can watch it for days…what’s not to like?!

What you’ll need

  • A clear grip seal bag
  • Sticky tape
  • Permanent marker pen
  • Blue food colouring
  • A glass of water
  • A window
  • Some sunshine!

How to make it

  1. Design your bag, including the sea, some clouds and the sun.
  2. Add a few drops of blue food colouring to the water.
  3. Pour the water into the bag (be careful to make sure the water does not touch the sides of the bag).
  4. Seal the bag securely and tape it to a window that sees a lot of sun.
  5. Come back after about 30 minutes: you should start to see some water droplets forming on the inside of the bag. Tap them to make it rain inside the bag!

What’s happening?

Since the Earth has a limited amount of water, it has to change around and around in something called the WATER CYCLE.

The water in the bag will get heated up by the sun and start to turn from liquid into gas. This is called EVAPORATION and is exactly what happens to the water in ponds, lakes and oceans.

This gas will then try to escape the bag, but as soon as it touches the sides it will cool down and turn back into liquid water. This is called CONDENSATION. Seeing little water droplets on the side of the bag tells you that this process is happening!

Condensation also happens after water evaporates from ponds, lakes and oceans. This usually happens high up in the sky but we know that it’s happening because this is how the clouds are made.

When the water droplets in your bag get too big, they will start to drip. This is called PRECIPITATION and also happens when water droplets within clouds get too big and fall to the ground…we call this rain!

 Did you notice?

The water you out in the bag was blue, but the droplets that formed due to condensation were clear. This happened because only the water evaporated and turned into gas: the food colouring was left behind in the blue mixture!

This is why rain water isn’t salty, even though most clouds are formed using evaporated sea water…




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