Nuclear–powered submarines Nuclear–powered engine requires no air. It works due to the heat generated by the fission of the nuclear fuel. This heat energy is utilized in converting water to steam and thereby to rotate the turbines of the engine of the submarine. Thus the submarine can stay submerged indefinitely, surfacing only when in need of supplies.

Sun′s nuclear fusion The sun shines as it converts energy from gravity into light. A huge amount of mass of hydrogen gas gets squeezed down from all sides, so tightly that four hydrogen nuclei combine to form one helium atom, in the core of the sun. This is called nuclear fusion. In the process some amount of mass of hydrogen atoms gets converted into energy in the form of light. The same process occurs in thermonuclear (fusion) bombs, with a slight difference. In the sun, the process occurs in a controlled manner but in a hydrogen bomb, it all happens in a big chain–reaction explosion, leading to destruction.

The great Caltech Physicist Richard Feynman, in a series of lectures given for Caltech undergraduates observed that if scientific history had to be reduced to one important statement it would be "All things are made of atoms" – little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another.

He also shared some of his thoughts standing at the seashore. "There are the rushing waves... Mountains of molecules, each stupidly minding its own business, trillions apart, yet forming white surf in unison. Deep in the sea, all molecules repeat the pattern of one another till complex new ones are formed. They make others like themselves... and a new dance starts. Growing in size and complexity, living things, masses of atoms, DNA, protein – dancing a pattern ever more intricate. Out of the cradle onto dry land here it is standing: atoms with consciousness; matter with curiosity – stands at the sea, wonders at wondering: I a universe of atoms, an atom in the universe."

At the boundary of the atom and on the outside, the behavior of electrons explains the features that Feynman thought were important. The nucleus is a ball of positive charge, surrounded by a cloud of negative charge which exactly balances the positive charge on the nucleus. But when another atom is on side of first atom, the electron cloud on the outside of second atom can only see half of the electron cloud of first atom shielding half of the positive charge inside. The atoms attract one another as each of the electron clouds experience the attraction from partially shielded nucleus of the other atom. But when the atoms get too close, in effect touching each other the negative charge on the clouds will repel them from each other. The two nuclei however are not affected as they are shielded from each other by a double layer of electrons. Quantum mechanical model of the atom is the best explanation that we have at this point but it is still changing and evolving.

The energy of the nucleus reveals itself in many ways; nuclear warheads that can destroy cities, submarines driven by nuclear reactors, nuclear power plants and in destroying cancerous cells. Nuclear energy comes from the conversion of mass and can result from nuclear reactions like fission (the splitting of the nucleus) and fusion (the coming together of nuclei).