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http://www.treccani.it/enciclopedia/forze-fondamentali_%28Enciclopedia-dei-ragazzi%29/

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Electromagnetism - Magnetic Force: The Four Fundamental Forces of Physics #4b

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Electromagnetism - Electrostatic Force: The Four Fundamental Forces of Physics #4a

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Gravitation: The Four Fundamental Forces of Physics #3

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Hank continues our series on the four fundamental forces of physics with a description of gravitation - the interaction by which physical bodies attract with a force proportional to that of their masses, and which is responsible for keeping planets in orbit, among other things.

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Weak Interaction: The Four Fundamental Forces of Physics #2

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Hank continues our series on the four fundamental forces of physics by describing the weak interaction, which operates at an infinitesimally small scale to cause particle decay. Watch the video on Strong Interaction: http://www.youtube.com/watch?v=Yv3EMq2Dgq8 Like SciShow on Facebook: http://www.facebook.com/scishow Follow SciShow on Twitter: http://www.twitter.com/scishow References: http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html#c4 http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html#c5

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Strong Interaction: The Four Fundamental Forces of Physics #1b

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Hank continues his primer on the strongest of the four fundamental interactions of physics, the strong interaction. Today he talks about the nuclear force and a force carrier called a pion. Like SciShow on Facebook: http://www.facebook.com/scishow Follow SciShow on Twitter: http://www.twitter.com/scishow References: http://science.howstuffworks.com/environmental/earth/geophysics/fundamental-forces-of-nature2.htm http://hyperphysics.phy-astr.gsu.edu/hbase/particles/expar.html#c1 http://cronodon.com/Atomic/Quark.html

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Strong Interaction: The Four Fundamental Forces of Physics #1a

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The Four Fundamental Forces Of Physics Explained

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What are the four fundamental forces of nature? | HowStuffWorks

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As you sit in front of your computer reading this article, you may be unaware of the many forces acting upon you. A force is defined as a push or pull that changes an object's state of motion or causes the object to deform. Newton defined a force as anything that caused an object to accelerate -- F = ma, where F is force, m is mass and a is acceleration.

The familiar force of gravity pulls you down into your seat, toward the Earth's center. You feel it as your weight. Why don't you fall through your seat? Well, another force, electromagnetism, holds the atoms of your seat together, preventing your atoms from intruding on those of your seat. Electromagnetic interactions in your computer monitor are also responsible for generating light that allows you to read the screen.

Gravity and electromagnetism are just two of the four fundamental forces of nature, specifically two that you can observe every day. What are the other two, and how do they affect you if you can't see them?

The remaining two forces work at the atomic level, which we never feel, despite being made of atoms. The strong force holds the nucleus together. Lastly, the weak force is responsible for radioactive decay, specifically, beta decay where a neutron within the nucleus changes into a proton and an electron, which is ejected from the nucleus.

Without these fundamental forces, you and all the other matter in the universe would fall apart and float away. Let's look at each fundamental force, what each does, how it was discovered and how it relates to the others.

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What are the four fundamental forces of nature?

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­As you sit in front of your computer reading this article, you may be unaware of the many forces acting upon you. A force is defined as a push or pull that changes an object's state of motion or causes the object to deform.

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The fundamental forces (or fundamental interactions) of physics are the ways that individual particles interact with each other. It turns out that for every single interaction observed taking place in the universe can be broken down to be described by only four (well, generally four-more on that later) types of interactions:

Gravity

Of the fundamental forces, gravity has the farthest reach but it's the weakest in actual magnitude.

It is a purely attractive force which reaches through even the "empty" void of space to draw two masses toward each other. It keeps the planets in orbit around the sun and the moon in orbit around the Earth.

Gravitation is described under the theory of general relativity, which defines it as the curvature of spacetime around an object of mass. This curvature, in turn, creates a situation where the path of least energy is toward the other object of mass.

Electromagnetism

Electromagnetism is the interaction of particles with an electrical charge. Charged particles at rest interact through electrostatic forces, while in motion they interact through both electrical and magnetic forces.

For a long time, the electric and magnetic forces were considered to be different forces, but they were finally unified by James Clerk Maxwell in 1864, under Maxwell's equations.

In the 1940s, quantum electrodynamics consolidated electromagnetism with quantum physics.

Electromagnetism is perhaps the most obviously prevalent force in our world, as it can affect things at a reasonable distance and with a fair amount of force.

Weak Interaction

The weak interaction is a very powerful force that acts on the scale of the atomic nucleus.

It causes phenomena such as beta decay. It has been consolidated with electromagnetism as a single interaction called the "electroweak interaction." The weak interaction is mediated by the W boson (there are actually two types, the W⁺ and W⁻ bosons) and also the Z boson.

Strong Interaction

The strongest of the forces is the aptly-named strong interaction, which is the force that, among other things, keeps nucleons (protons and neutrons) bound together. In the helium atom, for example, it is strong enough to bind two protons together despite the fact that their positive electrical charges cause them to repulse each other.

In essence, the strong interaction allows particles called gluons to bind together quarks to create the nucleons in the first place. Gluons can also interact with other gluons, which gives the strong interaction a theoretically infinite distance, although it's major manifestations are all at the subatomic level.

Unifying the Fundamental Forces

Many physicists believe that all four of the fundamental forces are, in fact, the manifestations of a single underlying (or unified) force which has yet to be discovered. Just as electricity, magnetism, and the weak force were unified into the electroweak interaction, they work to unify all of the fundamental forces.

The current quantum mechanical interpretation of these forces is that the particles do not interact directly, but rather manifest virtual particles that mediate the actual interactions. All of the forces except for gravity have been consolidated into this "Standard Model" of interaction.

The effort to unify gravity with the other three fundamental forces is called quantum gravity. It postulates the existence of a virtual particle called the graviton, which would be the mediating element in gravity interactions. To date, gravitons have not been detected and no theories of quantum gravity have been successful or universally adopted.

Edited by Anne Marie Helmenstine, Ph.D.

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Know the Four Fundamental Forces of Physics

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The fundamental forces (or fundamental interactions) of physics are the ways that individual particles interact with each other. It turns out that for every single interaction observed taking place in the universe can be broken down to be described by only four (well, generally four-more on that later) types of interactions: Of the fundamental forces, gravity has the farthest reach but it's the weakest in actual magnitude.

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A free neutron will decay by emitting a W⁻, which produces an electron and an antineutrino.

When a neutrino interacts with a neutron, a W⁻ can be exchanged, transforming the neutron into a proton and producing an electron.

This interaction is the same as the one at left since a W⁺ going right to left is equivalent to a W⁻ going left to right.

A neutron or proton can interact with a neutrino or antineutrino by the exchange of a Z ⁰.

One of the four fundamental forces, the weak interaction involves the exchange of the intermediate vector bosons, the W and the Z. Since the mass of these particles is on the order of 80 GeV, the uncertainty principle dictates a range of about 10⁻¹⁸ meters which is about .1% of the diameter of a proton. The weak interaction changes one flavor of quark into another. For example, in the neutron decay depicted by the Feynman diagram at left above, one down quark is changed to an up quark, transforming the neutron into a proton.

The primitive vertices in the Feynman diagrams for the weak interaction are of two types, charged and neutral. For leptons they take the following form

The electron is used as an example in these diagrams, but any lepton can be substituted on the incoming side. The exit side (top) will be the same for the neutral vertex, but determined by the charge of the W in the charged vertex. Besides conserving charge, the vertex must conserve lepton number, so the process with the electron can produce an electron neutrino but not a muon neutrino.

The neutral interaction is simpler to conceive, but rarely observed because it competes with the much stronger electromagnetic interaction and is masked by it.

The charged vertices in the weak interaction with quarks take the form

So it is seen that the quark changes its flavor when interacting via the W⁻ or W⁺. As drawn, this interaction cannot be observed because it implies the isolation of an up quark. Because of quark confinement, isolated quarks are not observed. But rotating the Feynman diagram gives an alternative interaction, shown below for both electron and muon products.

This suggests the weak interaction mechanism for the decay of the pion, which is observed to happen by the muon pathway.

The weak interaction in the electron form at left above is responsible for the decay of the neutron and for beta decay in general.

Index

Fundamental force concepts

Reference
Kaufmann
Ch. 29

Griffiths
Ch 2

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A free neutron will decay by emitting a W-, which produces an electron and an antineutrino. When a neutrino interacts with a neutron, a W- can be exchanged, transforming the neutron into a proton and producing an electron.