Jose F. Moreno/The Associated Press
Let’s Talk Science and the Royal Society of Canada have partnered to provide Globe and Mail readers with relevant coverage about issues that affect us all – from education to the impact of leading-edge scientific discoveries. Let’s Talk Science offers a number of fun activities to get youth engaged in STEM.
Make a model of the water cycle and find out how water moves around on planet Earth.
What You Need
● Large container with a flat bottom
● Small glass or jar
● Table salt
● Plastic wrap
● Elastic
● Weight or rock
● Warm water
● Light/heat source
● A safe place to leave the container for 1-2 days under light/heat source
What to Do
*Safety first! Never leave an electric heat source unattended. Keep all flammable objects away from an electric heat source.
- In the large container, dissolve some salt in one or two inches of warm water. Use enough salt to make the water taste salty (test by dipping in your finger and tasting).
- Place the glass or jar in the centre of the large container, making sure it doesn’t tip over in the water. Make sure the top of the glass is a few inches lower than the top of the large container.
- Cover the top of the large container loosely with plastic wrap and secure it around the edges of the container with an elastic band. Make sure the entire top is covered and no air can get in or out.
- Place the weight or rock on top of the plastic wrap directly above the glass.
- Place the apparatus under the sun or a light/heat source for a day or two.
What’s happening?
The heat will cause the water at the bottom of the large container to evaporate. It will condense and collect on the surface of the plastic wrap (like a cloud), and then it will run down to the lowest point of the plastic, under the weight or rock and will drip into the glass (like rain). The salt, however, will not evaporate with the water and so, the water in the glass should taste clean. This is why rain is fresh and not salty, even if it comes from seawater.
Why does it matter?
When the sun heats the oceans, the water vapour that forms rises to cooler temperatures and condenses as clouds. Air currents circulate these clouds around the globe. Eventually, so much water condenses that the clouds become heavy and precipitation is released, usually in the form of rain. This process is known as the water cycle.
Precipitation, like rain, snow, and mist, is an important source of fresh water. Only about 2.5% of the Earth’s water is fresh water. Of that 2.5%, most are frozen in glaciers or are present as ground water. This leaves only 0.001% of the world’s water accessible for drinking. Without freshwater precipitation, like rain, available basins of fresh water, such as lakes and rivers, would dry up.
Investigate further
● Check the apparatus frequently while under the light/heat source. What happens to the salt water?
● Taste any water that forms inside the glass. What do you think has happened to the salt water?
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