初三休整阶段英语练习.doc

D（东城） You have learned about energy. Do you know that HEAT is a form of ENERGY? Yep, this form of energy acts on everything. And, we’re going to look at a few experiments to learn how this form of energy acts and why we need to know all about it. The heat energy of something is decided by how active its atoms(原子)and molecules(分子)are. A hot object is one whose atoms and molecules are excited and show rapid movement. A cooler object’s molecules and atoms will be less excited and show less movement. When these guys are in the excited state, they take up a lot of space because they’re moving around so fast. When the atoms and molecules settle down, or cool down, they take up less space. If a HOT high-energy atom comes into contact with a cool low-energy atom, the excited atom will loose some of its energy to the cool atom. The two atoms will reach an energy level that’s between where they each started out. That level is called Thermal Equilibrium. Experiment: If you have a cup of really hot chocolate and want to cool it down, you may put an ice cube in the cup. After the ice has completely melted (disappeared), the hot chocolate and the melted ice have come to Thermal Equilibrium. Now that you have an idea of what heat is, let’s look at some of the effects of this form of energy. Here’s another experiment. Blow up a balloon, but not all the way. Put the balloon in a refrigerator for about an hour, then take it out. Did it become smaller? Why? It became smaller because the air molecules inside the balloon slowed down and are taking up less space. Now put the balloon in direct sunlight. What happened after it warmed up? Why? From the above experiment, we learned a very important fact—heat causes things to “grow”. We call this Thermal Expansion. If things “grow” when heated, what do you think happens to them when they get cold? If you get a chance to check out some railroad tracks, notice the gaps or separations between the rails. (Don’t get run over by a train