Not only does what we see exist, since gases are not visible. Matter can be in a solid, liquid, or gaseous state. We can produce changes in state by changing the temperature. Density is the relationship between weight and volume. Density has been important in experiments, such as when carbon dioxide sank to the bottom of the glass because it is denser than oxygen.
We have learnt how to make a closed electrical circuit because it must be a closed circuit for the experiment to work. We have also learnt that if they are of the same pole, they repel each other, and if they are of different poles, they attract each other. The Earth acts as if it had a magnet running through it, with the south pole of the magnet located near the planet's geographic north. Since opposite poles attract each other, the north pole of a magnetised needle points in that direction.