1. Take a piece of chalk, let the students look at it, break it from the middle (be careful not to grind the cross section), and then connect the two pieces of chalk together. Hold the two ends of the chalk and squeeze, so that a certain pressure is generated at the stubble, and slowly release, the two sections can be combined together, and hold one end to show the students. When it is shaken lightly, it will not break again, which is enough to show that there is an attraction between molecules (because chalk is dry and non-sticky material, it will not make students misunderstand like plasticine). Writing on the blackboard with chalk shows that there is also gravitational force between the blackboard and the chalk molecules, so it can be shown that the intermolecular gravitational force exists not only between the same kind of molecules, but also between different kinds of molecules.
2. Turn the chalk at an angle and press it again, it is not easy to catch. The reason is that most of the molecular spacing is greater than 10r0, and there are not many molecular spacings close to 10r0, so the gravitational force is not enough to make them fit together, so it can be shown that the molecular spacing is greater than The molecular force is negligible at 10r0.
3. Use easy-to-find chalk to simultaneously illustrate the existence of gravitational forces between molecules and the circumstances under which molecular forces can be ignored. In addition, the experiment can be carried out together with the students, summarizing while experimenting, and an abstract and boring class can be successfully completed in a relaxed and active atmosphere.
