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Four forces are understood to govern the universe: the strong and weak nuclear forces, the electromagnetic — or electrical — force, and gravity. The latter two types, electrical force and gravity, are the only of these forces that extend to a macro range and therefore interact with matter on a large scale. Electromagnetism is responsible for chemical reactions, light, vision and virtually all interplay of matter. Almost all technology requires electricity to function, and there are several vital aspects and measurements of the electrical force. The basis of this force is the movement of electrons and the workings of positive and negative electrical charges.
Particles of matter can have positive or negative electical charges. Protons, which form the nucleus of an atom, have a positive charge, whereas the electrons that orbit the nucleus have a negative charge. Opposite charges attract one another in an effort to neutralize charge, and like charges repel, so putting opposite poles of two magnets together causes the ends of the magnets to pull toward one another. Electricity, at its most basic form, is the movement of electrons from one location to another in a static discharge or in an electronic circuit; electricity can only flow where there is an available conductive path.
The electromagnetic force is so named because an electric current and a magnetic field can create each other. Passing a magnet through a coil of wire causes the electrons in the wire to move away from the magnet due to the repulsion of the electrical force. Similarly, running an electric current through a coiled wire produces a magnetic field whose direction is opposite the current due to electrical inertia.
Two main measurements of electrical force govern most of the behavior that electricity exhibits when interacting with objects: voltage and resistance, from which the measurement for current derives. Voltage is the amount of electrical potential that exists from one point to another, similar to the pressure built up inside an activated water hose. The higher the voltage between two points is, the greater the electrical pressure and the more easily current will flow. The concept of resistance describes an object's propensity to resist electrical flow. The electrical current in amperes that flows from one point to another can be expressed as the voltage divided by the resistance in ohms.
Electrical current is either alternating current or direct current. The difference is the direction of flow; alternating current switches directions dozens of times per second with reversed polarities. Direct current maintains polarity and therefore only flows in one direction, such as through a battery.