The third force is called the nuclear force . As its name suggests, it is the force which hold the particles in the nucleus of an atom together. It is the strongest of the three forces. In fact, it's so strong that it takes very fancy machines, capable of producing nuclear power, to get the nuclear force to release its grip. There is an amazing and limitless source of energy.
Atoms are the building blocks of the universe.
Everything is made up of atoms and atoms are extremely small. In fact, there are millons of atoms lurking in the period at the end of this sentence. The most common atoms are hydrogen and oxygen. These atoms are gases that make up most of the air we breath. Carbon is also a very common atom and it helps to make up the solid backbone of living things.