Atoms(原子) are all around us. They are the bricks of which everything is made. Millions of atoms are held in just one grain of salt , but in spite of their small size they are very important. The way an everyday object acts depends on what kind of atoms are in it and how they act . For example, you know that most solid objects melt(熔化) if they get hot enough. How doesit happen? It is the effect of the heat on the object’s atoms. All atoms move constantly. When they are hot, they move faster. Usually the atoms in an object hold together and give the object its shape. But if the object grows hot, its atoms move so fast that they break the force that usually holds them together. They move out of their usual places so that the object loses its shape. Then we say that the object is melting.