Let's take a little side trip into the furnace where atomic nuclei are created. The nuclear force, the force that binds nucleons inside a nucleus, is a strong force. It is pretty "blind" though: Two nucleons won't notice the effect of the force until they are very close together, close enough to "touch". The electric force, the force that makes two protons go away from each other, however, can see very well indeed. One look is all it takes, and the protons know they don't like each other. So naturally, they never get close enough to feel the nuclear force.

So what we need to make a nucleus is a furnace. A place where protons have so much energy that they bump together despite their positive charges. Check out the animation below. With the slider you can adjust the amount of energy the protons get. If they have enough energy, the nuclear force (the gray field) will hold them together. Otherwise, the electric force will send them apart without giving them a chance for a closer contact.

In nature we find furnaces that can fuse together protons and neutrons in the stars. There's plenty of energy in the stars to bring nucleons together, and once they're together they give away the energy they don't need anymore and it can be used to fuse more nucleons. Some energy is also lost to the star and a tiny fraction travels all the way to our earth. Here we can see the energy as light and feel it as heat.

Light and heat are also made up of particles, the photons. Photons are probably the particles of whose effect we take the most notice. Depending on how much energy they have, we recognize them as different things. By moving the photon on the right you can see how we experience photons in our lives.

The photon has a very important job as the force carrier particle of the electric force. It carries out this function when it only has some "borrowed" energy! You can read more about this special job of the photon by the virtual particles .

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