Lesson Summary:
The lesson builds on the children’s understanding of evaporation and precipitation, introduces them to the conditions necessary for the formation of snow, and to the different types of snowflakes. Activity A tests their understanding of the information given in the reading while Activity B requires them to describe the formation of snow in their own words in a creative exercise.
Objectives:
- The children will understand and be able to explain how snowflakes are formed.
- The children will know, and be able to describe the different categories of snowflakes.
Subject Area:
Science
Lesson Excerpt:
We all know that when water evaporates it gathers into clouds in the form of water vapour. When the conditions are right the water falls to the ground again – this is called precipitation. Rain, hail, sleet and snow are all forms of precipitation. Although they all originate from the same place – the clouds - they are caused by different atmospheric conditions.
Snow is formed when water vapour in the clouds comes into contact with a small particle, such as dust. At below freezing temperatures, the water vapour changes into ice crystals which form around the dust particle. This change is known as deposition, or desublimation, in other words, the vapour changes from a gas to a solid without becoming a liquid, which would have fallen as rain (The opposite process, where a solid changes to directly to a gas is called sublimation). So the first condition for snow to fall is that the temperature of the clouds must be sub-freezing.
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