Can you rank the four forces that affect the structure of an atom in order from the strongest to the weakest?

2 Answers
Nov 18, 2017

Strongest to weakest, they are: Strong force, electromagnetism, weak force, gravity. But see my discussion below..


This comparison is a bit more complicated than we might think, as the two nuclear forces act very differently from the more familiar electromagnetic and gravitational forces. While the latter two decrease as #r^2# with increasing distance, the strong nuclear force actually increases in strength with distance, while the strength of the weak force is rather difficult to pin down at all, as it practically vanishes at distances even as large as a proton. (This rapid decay in strength is due to the high mass of the W particle.)

Also, gravity and electromagnetism extend essentially to infinite distances, while the nuclear forces (and especially the weak force) are confined to distances similar to or less than that of the nucleus.

The result is, that if you are talking very short distances, the above list - strong force, electromagnetism, weak force, gravity should be altered to become

Strong force, weak force, electromagnetism, gravity.

Here are two sites you should check out. The first just gives a numerical sense of the relative strengths, while the second is a very in-depth discussion of the issue!

Nov 19, 2017

The relative strengths of the four funndamental forces is very dependent on the distances involved.


The four fundamental forces are very different and each has an important role to play. In fact two of the fundamental forces are actually not forces.

Gravity behaves like a force as Newton described. In fact it is not a force. Mass, energy and momentum cause four dimensional spacetime to curve. Curved spacetime tells matter how to move. At the scale of large objects gravity rules supreme over the other forces. At the scale of an atom, the energies are so small that gravity has a negligible effect.

The electromagnetic force describes the interactions of charged particles. It also describes light. Stars and other massive objects output vast amounts of electromagnetic radiation. At the scale of the atom, electromagnetism rules supreme over the other forces. It describes how electrons move and the chemistry of elements.

When it comes to the atomic nucleus it is a battle ground between the electromagnetic and strong and weak nuclear forces.

Actually neither the strong or weak nuclear forces are true forces. The weak force is not a force in the usual sense. The strong force is actually a residual effect of the colour force which binds quarks into protons and neutrons which extends out of the protons and neutrons to bind them together.

At the scale of the atomic nucleus, the strong force has to be the strongest. The electromagnetic force is long ranged. Every proton in a nucleus repels every other proton. The strong force is able to overcome the electromagnetic force at short range. It can strongly bind adjacent protons and neutron and hold a nucleus together. All nuclei with more than 82 protons are unstable as the short range strong force loses to the long range electromagnetic force.

The weak force acts as a kind of peacekeeper between the strong and electromagnetic forces. It isn't really a force. It is also very slow acting as it is mediated by the heavy W bosons. A nucleus can be unstable because it has either too many neutrons or too many protons. The weak force corrects this by converting a proton into a neutron or vice versa. This is beta radiation.