We were cornered in a sort of way already. But these butchers up the cavern had been surprised, they were probably scared, and they had no special weapons, only those little hatchets of theirs. And that way lay escape. Their sturdy little forms--ever so much shorter and thicker than the mooncalf herds--were scattered up the slope in a way that was eloquent of indecision. I had the moral advantage of a mad bull in a street. But for all that, there seemed a tremendous crowd of them. Very probably there was. Those Selenites down the cleft had certainly some infernally long spears. It might be they had other surprises for us.... But, confound it! if we charged up the cave we should let them up behind us, and if we didn't those little brutes up the cave would probably get reinforced. Heaven alone knew what tremendous engines of warfare--guns, bombs, terrestrial torpedoes--this unknown world below our feet, this vaster world of which we had only pricked the outer cuticle, might not presently send up to our destruction. It became clear the only thing to do was to charge! It became clearer as the legs of a number of fresh Selenites appeared running down the cavern towards us.

What are two reasons that the narrator decides the only option is to charge?

Light rays strike a reflecting surface. They are then reflected back. You can predict the angle of the reflected light. Imagine a ball bouncing off a surface. Light can do the same thing. That is, assuming the surface is shiny. So how do you know where light will go after it strikes a shiny surface? It depends on how the light initially strikes the shiny object. Light does not always go straight toward a surface. Therefore, not all light bounces straight back. Sometimes, light can hit a surface at an angle. The angle at which it strikes the surface tells us how it will bounce off. While light is different to a ball, they react in a similar manner. Many sports rely on knowledge of reflection. Pool players know a lot about reflection. They take great care when they strike the pool ball. They need it to go to a certain place. They know the angle it will hit the side of the pool table.

What has to be true in order to use a knowledge of reflection to help in sports?

The properties of matter depend on the types of atoms that matter is made of. Matter can exist in two forms. It can be a pure substance. This means it is not mixed with anything. It can also be a combination of different substances. This means it can be a mix of different types of atoms. You may recall that atoms differ based on the numbers of protons they contain. Some atoms contain only one proton such as Hydrogen. Other atoms contain many protons. There are many types of atoms. For example, Helium has two protons. An Oxygen atom has eight. Water is composed of a two types of atoms. Water is made of two Hydrogen atoms and one Oxygen atoms. There are only so many types of atoms. These atoms can be mixed into an almost limitless amount of substances. So what do we call a substance that has only a single type of atom?
What form of matter is not mixed with anything?