什么是重力？
Section outline
-
Some people jump out of planes.
They fall.
This is sky diving.
A lot of people sky dive.
::有些人从飞机上跳下来。他们下降。这是跳伞。很多人都跳伞。
Planes are pulled to the Earth.
A force pulls them down.
A force is a pull.
This force is gravity.
We do not see it pull.
We can see the effects of it.
Things fall down.
::飞机被拉向地球。一个力把它们往下拉。力就是拉力。这个力就是重力。我们没有看到它拉扯。我们可以看到它的影响。东西会掉下来。
Look at the sky diver.
Do you see him fall?
We do not see gravity.
It is what pulls him down.
::看那个跳伞运动员。你看到他摔倒了吗？我们看不见重力。这就是把他拖下水的原因。
What are things that fall?
A ball will fall.
A toy plane falls.
Rain falls.
What things will fly?
The bird can fly.
The bird must land to rest.
Things that fly must still land.
Gravity pulls on the bird.
::什么东西会掉下来？一个球会掉下来。一架玩具飞机掉了下来。雨落。什么东西会飞？这只鸟会飞。鸟儿必须着陆休息。会飞的东西还得着陆。重力拉着鸟。
Gravity can pull over a long way.
It holds the Moon in place.
The Sun has gravity too!
The Earth goes around the Sun.
The Sun holds Earth in place.
The Sun pulls on all the planets.
::重力可以把我们拉过来很远。它支撑着月球。太阳也有引力！地球绕太阳转。太阳支撑着地球。太阳吸引着所有的行星。
What if there was no gravity?
We could not play games.
Plant roots would not grow down.
::如果没有重力会怎样？我们不能玩游戏。植物的根不会向下生长。
Pour a drink.
What does it do?
It goes down to the cup.
Gravity keeps it there.
Do you have a book on your desk?
What holds it there?
We can throw away trash.
With no gravity, it would float.
That would be bad!
::倒一杯饮料。它是做什么的？它下到杯子。重力使它保持在那里。你桌上有一本书吗？是什么把它固定在那里的？我们可以扔掉垃圾。没有重力，它会浮起来。那太糟糕了！
1. What are some things that fall?
2. Why do things fall?
3. How can you stop something from falling?
::1. 什么东西会掉下来？2. 为什么东西会掉下来？3. 你怎么能阻止东西掉下来呢？
