WRITE IT RIGHT (p.83)
Brainstorm the topic with your students. The topic is familiar to them. So they
54 can add other interesting ideas about water properties.
Like air, water is found almost everywhere. It is familiar to us in different forms, as drinking water, water vapour, ice and snow.
Water has some surprising qualities. For example, most liquids freeze and become denser, but water becomes lighter. When you fill a pan of water, with ice cubes, you note that unmelted particles remain on the surface. The reason is that frozen water is lighter than water in liquid form. When water expands, it becomes ice and it exerts pressure. If you fill a glass bottle and put it in the freezer, the bottle breaks. As the frozen water expands, it exerts pressure on the glass bottle.
Water molecules have a strong attraction to each other. The force of attraction is called cohesion. If you moisten two pocket mirrors and stick them together, you will not be able to pull them apart. The water molecules on the surface of the pocket mirrors attract each other. But it is not difficult at all to separate dry mirrors because ...
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2014-02-07, 16:18
العرض العادي
