Try This At Home

Rain Bottles

You will need

  • Empty plastic bottles with lids
  • Something to make holes in the lids
  • Water

What To Do

  1. Put a few holes in the bottom of the bottle and one in the lid. Don’t make the holes too big, otherwise the surface tension won’t hold the water in the bottle.
  2. Fill the bottle with water and put the lid on. Hold it over the sink or in the bath.
  3. When you put your finger over the hole on the lid of the bottle no water comes out of the bottle.
  4. When you lift your finger off the hole the rain flows out!

What’s happening?

  • The water is held inside the bottle by a combination ofair pressure and the surface tension of the water.
  • When you cover the hole in the lid, air can’t get in to fill the empty space. The air pressure inside the bottle drops a little. The higher air pressure around the bottle pushes against the bottle walls and against the holes in the bottom of the bottle. This stops any more water escaping. The surface tension of the water droplets also helps to seal the holes in the bottom of the bottle.
  • When you take your finger off the lid hole, gravity attracts the water downwards. As water leaves the holes in the bottom of the bottle, air flows in through the lid’s hole to take up the space being created.

Discover More

  • Do you think it will work if we use bigger or smaller bottles?
  • What happens if you put the holes in the side of the bottle?

Did You Know

Water has something called “surface tension”. Surface tension means that water molecules are always pushing and pulling each other which makes the water stick to itself and it takes some effort to pull water-drops apart.