重力

Lesson Objectives
::经验教训目标

• Explore the Law of Gravity by demonstrating that gravity is a force that can be overcome. 
  ::通过证明重力是一种可以克服的力量来探索重力法则。

Lesson Vocabulary
::词汇表课程

• force
  ::强力力力

• gravity
  ::重力

 

How would the universe look without gravity? It would have no planets and no stars. That's how it looked when it was young. When the universe was young, there was only gas and dust. From this gas and dust, everything we now see was made. How were stars and planets created from just gas and dust? 
::宇宙没有引力会如何看?它没有行星,没有恒星。当它年轻时,它就是这样看的。 当宇宙还年轻时,它只有气体和尘埃。从气体和尘埃中,我们所看到的一切都是由气体和尘埃形成的。恒星和行星是如何由气体和尘埃创造的呢?

The answer is gravity. The same gravity that holds you down on Earth. The same force that causes your pencil to roll off your desk. The same force that causes it to fall to the floor. The invisible force of gravity caused dust and gas particles to be pulled together. This force is what formed all the objects in our solar system. This force formed the smallest moons. It also formed our Sun. This force caused more than just our solar system to form. It caused  all  the other solar systems to form. It caused the formation of all the galaxies of the universe.  
::答案是引力。 同样的引力将您压在地球上。 同样的引力导致您的铅笔从桌上滚下来。 同样的力导致它掉到地板上。 无形的引力导致灰尘和气体粒子被拉在一起。 这股力形成了太阳系中的所有物体。 这股力组成了最小的月亮。 这股力也形成了我们的太阳。 这股力不仅导致太阳系的形成, 也导致了其他所有太阳系的形成。 它导致了宇宙所有星系的形成。

Defining Gravity
::重力定义

Gravity  is a force, but not like other forces you may know. Gravity is a bit special. You know that a force is a push or pull. If you push a ball, it starts to roll. If you lift a book, it moves upward. Now, imagine you drop a ball. It falls to the ground. Can you see the force pulling it down? That is what makes gravity really cool. It is invisible. Invisible means you cannot see it. But wait, it has even more surprises.
::重力是一股力量, 但不像你可能知道的其他力量。 重力有点特殊。 您知道, 重力是一种推力或拉力。 如果您推球, 它就会开始滚动。 如果您抬起一本书, 它会向上移动。 现在, 想象一下, 你扔下一个球。 它会掉到地上。 你能看到它被拉下来的力吗 ? 这就是引力真正冷却的原因。 它是隐形的。 不可见的意味着你看不到它。 但是, 等待着, 它会有更多的惊喜 。

Gravity holds planets in place around the Sun. Gravity keeps the Moon from flying off into space. Gravity exerts a force on objects that are not even touching. In fact, gravity can act over very large distances. However, the force does get weaker the farther apart the objects are. 
::引力把行星放在太阳周围。 引力使月球无法飞入太空。 引力对甚至没有触碰的物体施加了力量。 事实上, 引力可以作用在很远的距离。 但是, 力确实变弱了, 距离物体越远, 力就越弱 。

Earth’s Gravity
::地球的重力

You are already very familiar with Earth’s gravity. It constantly pulls you toward Earth's center. What might happen if there was no gravity?
::您已经非常熟悉地球的引力。 它不断将您拉向地球的中心。 如果没有引力,会发生什么?

You know that the Earth is rotating on its axis. This motion causes our day and night cycle. The Earth also orbits the Sun. All this motion may cause you to fly off the Earth! You can thank gravity for keeping you in place.
::你知道地球在轴上旋转。 这个运动导致我们的昼夜循环。 地球也在太阳的轨道上运行。 所有这些运动都可能导致你飞离地球! 你可以感谢引力让你保持原位。

Gravity keeps us firmly down on the ground. Gravity also pulls on objects that are in the sky. It also pulls on objects that are in space. Meteors and skydivers are pulled down by gravity. Gravity also keeps the moon orbiting the Earth. Without gravity, the moon would float away. It also holds artificial satellites in their orbit. Many of these satellites help to connect the world. They allow you to pick up a phone a call in many parts of the world. You can also thank gravity for all your TV channels. Gravity keeps Earth and the other planets moving around the much more massive Sun.
::引力使我们在地面上稳定下来。 引力还拉动着在天空中的物体。 引力还拉动着在太空中的物体。 气象和天体被引力拉下。 引力也使月亮绕地球运行。 没有引力, 月亮会飘走。 月球也会在它们的轨道上持有人造卫星。 许多这些卫星有助于连接世界。 它们允许你在世界许多地方接听电话。 您也可以感谢电视频道的引力。 引力让地球和其他行星绕着大得多的太阳运行。

How Can Gravity Be Overcome?
::重力如何克服?

"What goes up must come down." You have probably heard that statement before. At one time this statement was true, but no longer. Since the 1960s, we have sent many spacecraft into space. Some are still traveling away from Earth. So it is possible to overcome gravity.
::”你可能听说过这个说法。有一次,这个说法是真实的,但不再是了。从1960年代开始,我们就把许多航天器送入太空。有些航天器仍在远离地球。因此,克服引力是可能的。

Do you need a giant rocket to overcome gravity? No, you actually overcome gravity every day. Think about when you climb a set of stairs. When you do, you are overcoming gravity. What if you jump on a trampoline? You are overcoming gravity for a few seconds. Everyone can overcome gravity. You just need to apply a force larger than gravity. Think about that the next time you jump into the air. You are overcoming gravity for a brief second. Enjoy it while it lasts. Eventually, gravity will win the battle.
::需要使用巨型火箭来克服重力吗? 不,你实际上每天都能克服重力。 想想当你爬上一套楼梯时, 你正在克服重力。 如果跳上踏板, 你将会克服重力几秒钟。 每个人可以克服重力。 你只需要应用比重力更大的力。 下次跳入空中时, 想想这个力。 您正在克服重力一秒钟。 享受它, 它会持续。 最终, 重力将赢得战斗 。

Lesson Summary
::经验教训摘要

• Gravity is the attraction between objects. These objects do not need to be touching. They can be some distance apart.
  ::重力是对象之间的吸引。这些对象不需要被触摸。它们可能相距很远。

• Earth’s gravity constantly pulls objects toward the center of the planet. Gravity also keeps moons and satellites orbiting Earth, and Earth orbiting the sun.
  ::地球的引力不断将物体拉向行星的中心。 引力还使卫星和卫星绕地球运行,地球绕太阳运行。

Lesson Review Questions
::经验回顾问题

Apply
::应用

1. What is the traditional definition of gravity?
   ::重力的传统定义是什么?

1. Identify factors that influence the strength of gravity between two objects.
   ::查明影响两个物体之间重力的因素。