Over the last few weeks, the sun
has finally been making an appearance in the sky. Could summer be
on it's way?
Just in case we do get a sudden
heatwave, we though we'd better show you how to cool your drinks
without a fridge (with the help of a great video from Questacon).
What you need:
- Small plastic drink bottles x2 - the bottles should be the same
size
- Toilet or kitchen paper
- Water at room temperature (make sure it's from the tap and is
suitable to drink!)
- Thermometer (optional)
- A windy day (or use an electric fan if it's not windy)
How to:
- Fill the drink bottles with water.
- Wrap one of the bottles in two layers of toilet or kitchen
paper.
- Wet the paper with water.
- Stand the two bottles next to each other. Put them outside if
it's a windy day. If it's not windy, put the fan on next to
them.
- After 20 minutes, take a sip of water from each bottle. Has the
temperature changed?
- Check the temperature every five minutes. You can guess the
temperature difference between the two bottles by tasting the
water, or use a thermometer to be accurate. Is the water from one
bottle cooler than the other?
What's happening?
The wet paper is acting as a refrigerator. The water evaporates
from the paper, cooling the water inside the bottle.
For water to evaporate, it needs enough energy to turn from a
liquid into a gas. When a molecule of water evaporates from the
paper, it takes some of the heat from its surroundings. Using a fan
or wind speeds up evaporation.
This is why we sweat when we're hot or doing exercise. Sweat
evaporating from the skin cools us down. As a molecule of sweat
evaporates from our body, it takes some of the heat from our body
with it.