Experiment of the Month:
Bottle with a Cap!

Here's a beautiful and simple experiment that you can do at home. It is inexpensive and lots of fun!

You will need:

  • Bottle. Use a fairly stiff plastic bottle, not the ones used for water.
  • A pin

Here is what you do:

  1. Make a small hole in the bottom of the bottle using the pin.
  2. Enlarge the hole using the nib of a ball point pen.
  3. Fill the bottle with water, holding your finger on the hole.
  4. Close the bottle with the cap and remove your finger from the hole.
  5. What do you see? Does the water come out?
  6. Open the cap a little. Does the water come out? Can you control how much water is coming out?
  7. What happens if you use a flexible bottle like a water bottle instead of a stiff bottle?

Here's what's happening:

When you closed the cap, there was no way for air to enter the bottle. Now, water can leave the bottle only if something else (in this case air) can take its place. Closing the cap meant this cannot happen, so the water stayed in the bottle.

When you opened the tap, you allowed some air to enter. As soon as this happened, water started flowing out. The amount of water that flows out depends on how much air is allowed inside, so you can use the cap as a tap!

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