Question: Electromagnetism is one of how many interactions in nature?
About the article "Electromagnetism", section "Abstract".

Candidate passages:
Electromagnetism, or the electromagnetic force is one of the four fundamental interactions in nature, the other three being the strong interaction, the weak interaction, and gravitation.
This force is described by electromagnetic fields, and has innumerable physical instances including the interaction of electrically charged particles and the interaction of uncharged magnetic force fields with electrical conductors.
The word "electromagnetism" is a compound form of two Greek terms, ἢλεκτρον, "ēlektron", "amber", and μαγνήτης, "magnetic", from "magnítis líthos" (μαγνήτης λίθος), which means "magnesian stone", a type of iron ore.
The science of electromagnetic phenomena is defined in terms of the electromagnetic force, sometimes called the Lorentz force, which includes both electricity and magnetism as elements of one phenomenon.
During the quark epoch, the electroweak force split into the electromagnetic and weak force.
The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life.
Ordinary matter takes its form as a result of intermolecular forces between individual molecules in matter.
Electrons are bound by electromagnetic wave mechanics into orbitals around atomic nuclei to form atoms, which are the building blocks of molecules.
This governs the processes involved in chemistry, which arise from interactions between the electrons of neighboring atoms, which are in turn determined by the interaction between electromagnetic force and the momentum of the electrons.
There are numerous mathematical descriptions of the electromagnetic field.
In classical electrodynamics, electric fields are described as electric potential and electric current in Ohm's law, magnetic fields are associated with electromagnetic induction and magnetism, and Maxwell's equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents.
The theoretical implications of electromagnetism, in particular the establishment of the speed of light based on properties of the "medium" of propagation (permeability and permittivity), led to the development of special relativity by Albert Einstein in 1905.
Following is a list of notable textbooks in electromagnetism. 
The action for electromagnetism is: formula_14  
The electromagnetic force is one of the four known fundamental forces.
The other fundamental forces are:  the weak nuclear force, which binds to all known particles in the Standard Model, and causes certain forms of radioactive decay.
(In particle physics though, the electroweak interaction is the unified description of two of the four known fundamental interactions of nature: electromagnetism and the weak interaction);  the strong nuclear force, which binds quarks to form nucleons, and binds nucleons to form nuclei  the gravitational force.
All other forces (e.g., friction) are ultimately derived from these fundamental forces and momentum carried by the movement of particles.
The electromagnetic force is the one responsible for practically all the phenomena one encounters in daily life above the nuclear scale, with the exception of gravity.
Roughly speaking, all the forces involved in interactions between atoms can be explained by the electromagnetic force acting on the electrically charged atomic nuclei and electrons inside and around the atoms, together with how these particles carry momentum by their movement.
This includes the forces we experience in "pushing" or "pulling" ordinary material objects, which come from the intermolecular forces between the individual molecules in our bodies and those in the objects.
It also includes all forms of chemical phenomena.
A necessary part of understanding the intra-atomic to intermolecular forces is the effective force generated by the momentum of the electrons' movement, and that electrons move between interacting atoms, carrying momentum with them.
As a collection of electrons becomes more confined, their minimum momentum necessarily increases due to the Pauli exclusion principle.
The behaviour of matter at the molecular scale including its density is determined by the balance between the electromagnetic force and the force generated by the exchange of momentum carried by the electrons themselves. 
The main focus of "JPSJ" is all topics related to physics.
This includes pure and applied physics research topics which encompass core physics disciplines, and broad topical coverage that is related to these core disciplines.
Hence, subject areas cover an exploration and investigation of nature and substances that exist in the world and the universe, from atomic to cosmological scales.
This encompasses defining and describing observations, interactions, and forces which occur in nature and, hence, in substances.
Such descriptions may include their effect on, or within, a given natural system.
More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.
Therefore subject areas encompass energy, forces, mechanics, radiation, heat, matter, electromagnetism, quantum mechanics and general theory of relativity.