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Although there are apparently many types of forces in the Universe, they are all based on four fundamental forces. The strong and weak forces only act at very short distances and are responsible for holding certain [[nucleons]] and compound nuclei  together. The electromagnetic force acts between [[electric charge]]s and the gravitational force acts between [[mass]]es. The [[Pauli exclusion principle]] is responsible for the tendency of [[atom]]s not to overlap each other, and is thus responsible for the "stiffness" or "rigidity" of matter, but this also depends on the electromagnetic force which binds the constituents of every [[atom]].

Although there are apparently many types of forces in the Universe, they are all based on four fundamental forces. The strong and weak forces only act at very short distances and are responsible for holding certain [[nucleons]] and compound nuclei  together. The electromagnetic force acts between [[electric charge]]s and the gravitational force acts between [[mass]]es. The [[Pauli exclusion principle]] is responsible for the tendency of [[atom]]s not to overlap each other, and is thus responsible for the "stiffness" or "rigidity" of matter, but this also depends on the electromagnetic force which binds the constituents of every [[atom]].

All other forces are based on these four. For example, [[friction]] is a manifestation of the [[electromagnetic]] force acting between the [[atom]]s of two surfaces, and the Pauli exclusion principle, which does not allow atoms to pass through each other. The forces in springs modeled by [[Hooke's law]] are also the result of electromagnetic forces and the exclusion principle acting together to return the object to its equilibrium position. [[Centrifugal force]]s are acceleration forces which arise simply from the acceleration of rotating [[frames of reference]].

All other forces are based on these four. For example, [[friction]] is a manifestation of the [[electromagnetic]] force acting between the [[atom]]s of two surfaces, and the Pauli exclusion principle, which does not allow atoms to pass through each other. The forces in springs modeled by [[Hooke's law]] are also the result of electromagnetic forces and the exclusion principle acting together to return the object to its equilibrium position. [[Centrifugal force]]s are acceleration forces which arise simply from the acceleration of rotating [[Frame of reference|frames of reference]].

There is currently some debate to whether there are five forces not four. The discovery of dark energy which acts on an even larger scale than [[gravity]] (with an opposing effect) and is a unique and separate force.  

There is currently some debate to whether there are five forces not four. The discovery of dark energy which acts on an even larger scale than [[gravity]] (with an opposing effect) and is a unique and separate force.