You don’t need a rainy day to make a rainbow -- in fact, it’s more fun on a sunny day. Go outside with your kids mid-morning or mid-afternoon; the sun needs to be at about a 45 degree angle to where you are standing for the best results. Get the kids to stand with their back to the sun. Turn on a hose that has an adjustable water sprinkler and adjust the nozzle until you have the effect of raindrops coming out from the hose. Make sure the sunlight is shining through the raindrops and you will see a rainbow form. This is because the water droplets refract the light and break it up into the colors you see when a real rainbow forms in the sky.
This raindrop project is something the kids can watch you do. Boil a pot of water, but make sure the kids are a safe distance away. When the water is boiling, put an upturned plate about 12 inches above the boiling water on a slight angle. The steam from the boiling water condenses on the cold plate and forms water droplets. The water runs to the edge of the plate and raindrops start to fall from the plate.
On a rainy day, get your kids to paint some abstract pictures using watercolor paints. They can be of anything that comes into their minds. The paintings don’t need to be recognizable as anything. Put the paintings outside in the rain and leave them so the raindrops fall onto the wet paint. When it stops raining, bring in the paintings and let them dry. Observe the wonderful patterns the raindrops have made to the paintings.
If it keeps on raining, then get your kids to measure the size of different raindrops. Put a layer of flour into the lid of a plastic container; something like an ice cream container lid works fine, or if you don’t have one, use the lid of a shoe box. Use a ruler so the flour is flat. Put the container outside in the rain for about 10 seconds and let about 20 raindrops fall into the container. Bring the container inside and empty the flour through a sieve. Give the sieve a shake and the dry flour falls through, leaving the raindrops coated in flour. Have the kids measure the size of the various raindrops. They will find they are all different sizes.