Hardness. Say: I wonder if (object) is hard. When we say the object is hard, we mean that when I scratch it with another sharp object there is no sign left on it. It is very difficult to leave traces on it. If the object is hard it means it is resistant to permanent shape changes. Do you think the leaf is hard? Let's make a hypothesis. I think it is not hard. Let us conduct an experiment in order to prove or disprove out hypothesis. We will need a coin for that. Take the leaf in the left hand and the coin in the right. Make sure your hands are in front of the baby's face so he can see well what is happening. Say: let's scratch the leaf with the coin. Do that. Say: let's observe now. What do you see? Do you see any lines left on the surface of the leaf? I dont see them. It means the object is very hard.
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