2012东城第一学期期末D篇
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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 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 state, they take up a lot of space because they
are 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 lose some of its energy to the cool atom. The two atoms will reach an energy level that’s
between where they reach 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 is 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!) Thermal expansion and contraction is why those gaps are
placed there that way, and why expansion joints are placed in long highway bridges. You have
probably felt expansion joints on old concrete highways. Remember the “thump-thump” sound
as you rode over them.
57. How many experiments are mentioned in the passage?
A. Two B. Three C. Four D. Five
58. What is Thermal Equilibrium?
A. The fact that hot atoms loose some energy to cool atoms when they meet.
B. The fact that there are always the gaps or separations between the rails.
C. The fact that the heat causes to increase in size.
D. The fact that heat is another form of energy.
