Physics Forces - Strong and Weak Nuclear

Question

What do people mean when they refer to Strong and Weak Nuclear forces in the context of 4 main forces in the universe?

Answer 1

well you know gravity and electromagnetic forces?

strong and weak nuclear forces are two more.  these four are the only four forces in the universe and account for all interactions

the range of these 2 are limited since the mediators (the particles that 'carry' the force) have mass...  they are called 'nuclear' because the forces can only act within a range about the size of a nucleus

Answer 2

The weak interaction (often called the weak force or sometimes the weak nuclear force[1]) is one of the four fundamental interactions of nature. In the Standard Model of particle physics, it is due to the exchange of the heavy W and Z bosons. Its most familiar effect is beta decay (of electrons in atomic nuclei) and the associated radioactivity. The word "weak" derives from the fact that the field strength is some 1013 times less than that of the strong force.

In particle physics, the strong interaction, or strong force, or color force, holds quarks and gluons together to form protons and neutrons.

The strong interaction is one of the four fundamental interactions, along with gravitation, the electromagnetic force and the weak interaction. Of the four fundamental forces, the strong interaction is the most powerful.

The strong force is thought to be mediated by gluons, acting upon quarks, antiquarks, and the gluons themselves. This is detailed in the theory of quantum chromodynamics (QCD

Answer 3

To cover the full details of the weak and strong nuclear interactions would require an under graduate textbook. However, I will attempt to present two brief summaries regarding the nature and properties of these two different nuclear forces. (Note: - for powers of 10, I will use the notation 10^...).

Starting with the weak nuclear force.

The Weak Force nuclear force is one of the four fundamental forces experienced by elementary particles. As its name suggests, the weak force is some 10 billion (10^10) times weaker than electromagnetism. The weak force operates in certain decay processes of elementary particles. The well-known radioactive decay processes of alpha and beta decay are mediated by the weak nuclear force. Since the weak interaction is both very weak and very short range, its most noticeable effect is due to its other unique feature: flavour changing. Consider a neutron (quark content: UDD, or one up quark and two down quarks). Although the neutron is heavier than its sister nucleon, the proton (quark content UUD), it cannot decay into a proton without changing the flavour of one of its down quarks. Neither the strong interaction nor the electromagnetic allow flavour changing, so this must proceed by weak decay. In this process, a down quark in the neutron changes into an up quark by emitting a W boson, which then breaks up into a high-energy electron and an electron antineutrino. Since high-energy electrons are beta radiation, this is called beta decay.

Due to the weakness of the weak interaction, weak decays are much slower than strong or electromagnetic decays. For example, an electromagnetically decaying neutral pion has a life of about 10^−16 seconds; a weakly decaying charged pion lives about 10^−8 seconds, a hundred million times longer. A free neutron lives about 15 minutes, making it the unstable subatomic particle with the longest known mean life.

The weak force, like the other fundamental forces, can be described in terms of the exchange of particles. In the case of the weak force, there are three particles that can be involved. Two of these particles are electrically charged: the W+ and the W-. The third particle is neutral and is called the Z0. All three particles

are bosons, meaning that they have zero spin. The W bosons have a mass of about 80 times that of the proton, while Z bosons have a mass about 90 times that of the proton. Due to the large mass of the weak interaction's carrier particles (about 90 GeV/c^2), their mean life is limited to about 3×10^−27 seconds by the uncertainty principle. Even at the speed of light this effectively limits the range of the weak interaction to 10^−18 meters, about 1000 times smaller than the diameter of an atomic nucleus.

Conservation of electrical charge implies that exchanging W's must give rise to a change in the charge, and therefore the identity, of the particles involved in the interaction. For example, if an electron neutrino (which is neutral) emits a W+, then to conserve charge the neutrino must change into a negatively charged particle. The rules governing the weak force dictate that this particle must be an electron. If a muon neutrino were to emit a W+, it would have to change into a negatively charged muon.

In 1979, the Nobel Prize for Physics was awarded to the US physicists Sheldon Glashow and Steven Weinberg and the Pakistani physicist Abdus Salam for showing how the weak force and electromagnetism are connected.

I will turn now to the strong nuclear interaction.

The Strong Force is also one of the four fundamental forces, experienced only by quarks and elementary particles made up of quarks. It is the interaction responsible for holding protons and neutrons together in the atomic nucleus. The strong force is the strongest of the four fundamental interactions, being approximately 100 times as strong as electromagnetism. It has the extremely short range of approximately 10^-15 m, less than the size of the nucleus. The strong force is 'carried' by particles called gluons; that is, when two particles interact through the strong force, they do so by exchanging gluons. Thus, the quarks inside of the protons and neutrons are bound together by the exchange of the strong nuclear force.

There are six basic types of quarks, called up, down, charm, strange, top, and bottom. The theory of the strong nuclear force is based upon the idea that each of these exists in three different varieties, called 'colours'—red, green, and blue to be exchanged in a force interaction. This has no connection with visible colour, but is simply a convenient label used to describe a property of the particles.

Just as the electromagnetic force can only be experienced by particles that carry an electrical charge, the strong force can only be experienced by particles that carry the 'colour charge'. Furthermore, just as electrical charge comes in two types that are labelled positive and negative, colour charge comes in three types, arbitrarily labelled as primary colours (normally - red, green, and blue) .

The strong force binds combinations of quarks to form particles called hadrons. The proton and neutron are hadrons, each containing three quarks. There is a strict rule that governs how the quarks bind together: the combination must be 'colourless'. Just as beams of red, green, and blue light mix to make white, or colourless light, the proton, for example, must have a red, a green, and a blue quark within it. This is the point of applying the colour metaphor to quarks. The set of all possible three-quark combinations form a class of hadron referred to as the baryons.

Every type of particle has a corresponding type of antiparticle, with opposite properties. Antiquarks have 'anticolour'. A combination of an anti-red, anti-blue, and an anti-green quark would also be 'colourless'. This combination forms the antiproton, which is an example of an antibaryon.

The third way to make a colourless combination is to bind a colour with its anticolour (for example, red with anti-red, blue with anti-blue, and so on). Such combinations are called mesons and are another class of hadron. The first mesons to be discovered were the members of the pion family.

The quantum theory of the strong force, quantum chromodynamics, has been highly successful in accounting for the properties of hadrons in terms of the exchange of gluons between quarks. Gluons travel at the speed of light and carry no electrical charge. Since they carry colour charge, they also feel the strong force, and may be capable of binding together into stable objects called glueballs.

The strong force has some curious properties. Over a short range its strength increases with distance between the quarks. While they are close together the quarks experience little force, but as they separate the force between them grows rapidly, pulling them back together. To separate two quarks completely would require far more energy than any possible particle accelerator could provide. Needless to say, that these brief summaries are incomplete due to the vast nature of the two interrelated topics.