There are several fundamental forces that hold our universe together.
One of these, of course, is gravity, the force between objects that have mass.
Another important force is the electromagnetic force.
The electromagnetic force is responsible for chemical reactions.
译文：有几种基本力将我们的宇宙维系在一起。其中之一，当然，是重力，存在于有质量的物体之间的力。另一个重要的力是电磁力。电磁力是产生化学反应的原因。
Without it, there would be no atoms or molecules.
Up until a couple of hundred years ago, very little was known about this force.
Learning about the electromagnetic force and how to use it was a major step forward.
It revolutionized communication, transportation and manufacturing.
Imagine what life would be like without electricity!
译文：没有电磁力，就没有原子或分子。直到几百年前，人们对这种力量知之甚少。学习电磁力以及如何使用它是向前迈进的重要一步。它彻底改变了通讯、运输和制造业。想象一下没有电的生活会是什么样子！
Question:
— Which of the fundamental forces is between objects that have mass?
— Gravity
Put the sentences below in order:
(1) One of these, of course, is gravity, the force between objects that have mass.
(2) The electromagnetic force is responsible for chemical reactions.
(3) Another important force is the electromagnetic force.
(4) There are several fundamental forces that hold our universe together.
Correct Order: (4) (1) (3) (2)
The electromagnetic force has two parts, the electric force and the magnetic force.
The electric force is the force between electrically charged particles such as electrons and protons.
Electric charges attract or repel each other with a force that depends on the distance between them.
The magnetic force is the force between magnetic poles, such as the north and south pole.
译文：电磁力有两部分，电力和磁力。电力是带电粒子(如电子和质子)之间的作用力。电荷相互吸引或排斥，其作用力取决于它们之间的距离。磁力是磁极之间的力，如北极和南极。
In fact, the Earth is like a large bar magnet, with a north and a south pole.
Many animals use the Earth's magnetic field to navigate during their migrations.
We can also see this magnetic field when we use a compass.
译文：事实上，地球就像一个巨大的有北极和南极的条形磁铁。许多动物在迁徙过程中利用地球磁场导航。当我们使用指南针时，我们也能看到这个磁场。
Questions:
1.— For what purpose do many animals use the Earth's magnetic field?
— for navigation
2.— Electrons and protons are examples of what?
— electrically charged particles
Repeat & Read Sentences:
1. Imagine what life would be like without electricity!
2. In fact, the Earth is like a large barmagnet, with a north and a south pole.
3. There are several fundamental forces that hold our universe together.
4. The magnetic force is the force between magnetic poles, such as the north and south pole.
Why does the Earth have a magnetic field?
Many scientists believe that the Earth's magnetic field is due to the Earth's rotation.
Deep inside the Earth is a solid iron core, surrounded by a liquid metal outer core.
The moving electric currents inside this liquid metal create a magnetic field.
译文：为什么地球有磁场?许多科学家认为地球的磁场是由地球的自转引起的。在地球的深处是一个固体铁核，被液态金属的外核所包围。液态金属内部流动的电流产生了磁场。
Question:
— What's deep inside the Earth?
— a solid iron core
The Earth's magnetic field is important because it protects us from the solar wind.
The solar wind is a current of charged particles coming at us from the Sun.
When the solar wind nears the Earth, the Earth's magnetic field deflects it away.
This protects the Earth from the radiation, which can be dangerous to life.
It also protects the satellites that we use for communication.
译文：地球的磁场很重要，因为它能保护我们免受太阳风的影响。太阳风是来自太阳的带电粒子电流。当太阳风接近地球时，地球的磁场就会使其偏离。这可以保护地球免受可能危及生命的辐射。它也可以保护我们用来通讯的卫星。
Exercises:
1.— What protects the Earth from the solar wind?
— The Earth's magnetic field
2. When the solar wind nears the Earth, the Earth's magnetic field deflects it away. This protects the Earth from the radiation, which can be dangerous to life.
Repeat & Read Sentences:
1. The Earth's magnetic field is important because it protects us from the solar wind.
2. The Earth's magnetic field protects the Earth from the solar wind.
3. Many scientists believe that the Earth's magnetic field is due to the Earth's rotation.
4. When the solar wind nears the Earth, the Earth's magnetic field deflects it away.