What we need:
- flask with lid, metallic works best,
- molding clay,
- Use the nail, and with the hammer punch a hole on the lid big enough for the straw. Don't let your child use the hammer;
- Fill the flask with water to 2/3, you can use juice;
- Close the flask with the lid;
- Place the straw in the hole;
- Seal the hole with the clay;
- Drink it, using the straw.
You can't drink. At beginning this looked a bit stupid right? But now you understand.
When we use the straw we don’t really think about what happens in the plastic tube, but the straw only works because the liquid we suck is replaced with air. In fact is all about pressure.
- When, in optimal conditions, we place a straw in a drink, the air pressure in the drink in exactly the same inside the liquid on the straw.
- When we pull the liquid up, we remove some air from inside the straw, and the pressure inside the plastic tube drops.
- While this is happening inside the straw the pressure on the surface of the liquid remains the same.
- This pressure variation, between surface and straw interior, makes the liquid to be pushed through the tube.
- If we close the flask, and prevent the air from circulating freely there is no way to create a pressure differential and therefore there isn't nothing to push the liquid into the straw!
The juice will stay there, until you unseal the jar!