Matter is made of atoms and molecules.
物质是由原子和分子组成的。
Water, for example, is the H2O molecule.
例如，水就是水分子。
This means that a molecule of water has 3 atoms.
这意味着一个水分子有3个原子。
A water molecule has two hydrogen atoms and one oxygen atom.
水分子有两个氢原子和一个氧原子。
Substances like sugar have many atoms in their molecules.
像糖这样的物质分子中有许多原子。
A molecule of sugar has many atoms, including carbon, hydrogen and oxygen.
糖分子有许多原子，包括碳、氢和氧。
Matter is made of molecules, such as H2O, which is the water molecule.
物质是由分子组成的，例如水分子。
Matter can be one of three states, solid, liquid or gas.
物质可以是固态、液态或气态三种状态之一。
Water and ice are the same substance, but they are in different states.
水和冰是相同的物质，但它们处于不同的状态。
These states depend on the temperature of the molecules.
这些状态取决于分子的温度。
When we heat a substance, the molecules move faster and try to take up more space.
当我们加热物质时，分子移动得更快，并试图占据更多的空间。
When we cool a substance, the molecules move more slowly.
当我们冷却物质时，分子移动得更慢。
When we cool a substance to its freezing point, it becomes a solid.
当我们把物质冷却到冰点时，它就变成固体。
In a solid, the molecules move very little.
在固体中，分子运动很少。
Their positions are almost fixed.
他们的位置几乎是固定的。
To be fixed means that their positions don’t change.
固定意味着他们的位置不变。
If we heat the molecules, they move faster and away from each other.
如果我们加热分子，它们移动得更快，彼此远离。
The solid begins to melt, like ice cream on a hot day.
固体开始融化，就像热天的冰淇淋。
At a certain temperature, a solid begins to change into a liquid.
在一定温度下，固体开始变成液体。
The temperature at which a solid changes into a liquid depends on the substance.
固体变为液体的温度取决于物质。
For water, the solid begins to change into a liquid when its temperature rises to about 0 degree Celsius.
对于水来说，当固体温度上升到0摄氏度左右时，它就开始变成液体。
For some substances, such as steel, the temperature at which it becomes a liquid is much higher.
对于某些物质，如钢，它变成液体的温度要高得多。
Steel often melts at around 1370 degrees Celsius.
钢通常在1370摄氏度左右熔化。
If we continue to heat a liquid, the molecules move even faster.
如果我们继续加热液体，分子移动得更快。
At a certain temperature, the liquid begins to change into a gas.
在一定温度下，液体开始变成气体。
For water, the liquid begins to change into a gas at 100 degrees Celsius.
对于水，液体在100摄氏度时开始变成气体。
That is the boiling point of water.
这就是水的沸点。
Inside a star, such as our Sun, the temperature is very high.
在恒星内部，比如我们的太阳，温度很高。
Everything inside the Sun is a gas.
太阳内部的一切都是气体。
According to scientists, there are over 65 elements inside the Sun.
据科学家称，太阳内部有65多种元素。
These include oxygen and iron.
其中包括氧气和铁。
Over 90 percent of the Sun is hydrogen gas.
超过90%的太阳是氢气。