Level 4 - Unit 1 - Part 2 Vocabu

A force is a push or a pull on an object. A force changes the motion of a moving object. A force can be strong or weak, and it always has a direction.
力是对物体的推或拉，可以改变物体的运动。力可强可弱，总是有方向。

The Earth is a planet that goes around the sun in a circular orbit. The Earth has a layer of gas above its surface which helps to support life.
地球是一颗沿着圆形轨道环绕太阳运行的行星。地球表面有一层气体，有助于维持生命。

Atoms are the building blocks of matter. At the center of an atom is its nucleus, which has a positive electric charge. Outside the nucleus are electrons, which have a negative charge.
原子是物质的组成部分，原子的中心是原子核，带正电荷，原子核外是带负电荷的电子。

Asteroids and comets are objects that orbit our Sun, but are smaller than planets. Asteroids that pass close to the Earth are called near-earth objects.
小行星和彗星也环绕太阳运行，但比行星小。靠近地球的小行星被称为近地天体。

The layer of gases just above Earth's surface is our atmosphere. The atmosphere is made up of gases such as oxygen and nitrogen. Without an atmosphere, there would be no life on Earth.
地球表面的气体层就是我们所说的大气层，大气由气体组成，如氧和氮。没有大气层，就没有地球上的生命。