Lesson25 Power
There is not enough petrol in the world for everybody now, and each year there is less, so what are we going to do when it finishes? Perhaps we will go back to horses and carriages and bicycles.
In the Second World War, some people did not use petrol in their cars. They made gas from wood and plants instead, and then they put it in big bags on top of their cars. The cars did not go fast, but it was better than nothing. We cannot cut down all our trees to make gas; we need them for other things too.
Besides gas, we can also use electricity for our cars, but first we must make the electricity! Some countries have coal, and they make electricity with that, but we will not always have coal. Other countries have great rivers, which turn turbines and generate electricity more easily and cheaply.
We are also able to get power from the tides. We put turbines in the mouth of a river. Then, when the tide comes up, it turns the turbines, and when it runs back towards the sea, it turns them again. We know that the waves of the sea can also turn turbines when they go up and down. Will all of these things generate our electricity in the year 2050?

petrol 汽油
turbine 水轮机
generate 发（电）

能源
现在世界上没有足够的汽油供应每个人，并且每年都在减少，那么汽油用完后我们打算怎么办？或许我们将回头使用马、马车和自行车。
在第二次世界大战中，有些国家的汽车不使用汽油。他们用树木和植物制造天然气，然后将天然气放进汽车顶上的大袋子里。这种汽车跑不快，但总比没有好。我们不能砍倒所有的树来制造天然气；我们还需它们做别的事情。
除了天然气，我们还可以在汽车上使用电能，但首先我们必须发电！有些国家有煤，因此他们用煤发电，但我们不会一直有煤。别的国家有大河，可以驱动水轮机发电，这比较容易和廉价。
我们也能从潮汐中获得能源。把水轮机放在河口，然后当潮水上涨的时候，它能驱动水轮机，而退潮时，又能驱动水轮机。我们知道大海的波浪在涨落时也能使水轮机旋转。所有这些能不能提供我们2050年所需的电力呢？