Molecular Movement in Liquid State : Development of Simple Model Experiments

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  • 液体状態における分子運動 : 簡単なモデル実験の開発
  • 液体状態における分子運動--簡単なモデルの実験
  • エキタイ ジョウタイ ニ オケル ブンシ ウンドウ カンタン ナ モデル ノ ジッケン

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Abstract

Most junior high school students have the misconception that molecules in a liquid state are not moving, but are stationary. To date, teaching molecular movement in a liquid state has been simply expository. There are very few practical works on this subject. Even when we use computer simulations, the teaching method is one-sided, and does not allow two way communication. To solve these problems, a sequence of model experiments has been developed, as follows. Exp. 1 Liquid assumes the shape of containers. Exp. 2 Liquid is passed through filter paper. Exp. 3 In liquid, some objects sink and others rise to the surface. Exp. 4 In liquid, diffusion occurs. These phenomena can be explained by a molecule model, such as grains of sand or rice. However, the static model of sand leads to inconsistency. A dynamic model is required to explain these phenomena. When students encounter phenomena that are inconsistent with the static model, they come to realize that grains of sand are not stationary; through discussions with their teacher, they deduce that water molecules are moving. In Exp. 3 and 4, Styrofoam balls (3 mm in diameter) are more effective models of water molecules. First, Styrofoam balls are dropped into a beaker. This type of Styrofoam ball is so small and light that each ball within the beaker moves randomly with a magnetic stirrer. It appears that each ball is moving on its own, because the stirrer is invisible. Second, some colored balls are dropped into the beaker and spread evenly throughout the beaker. In this connection, the Styrofoam balls rub against each other, with the result that they become charged and often hop up. To eliminate static electricity, antistatic spray is used on the surfaces of the balls before hand. This is a very persuasive method, which has a great visual appeal for students, and which is effective in producing conceptual change.

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