There are four fundamental forces:

• gravity
• electromagnetic force
• strong nuclear force
• weak nuclear force

Exchange particles, or bosons, are used to explain the interactions of these forces.

Gravity – gravitons

A particles which consists of mass will attract other particles with the force of gravity. How this attraction works is due to bosons known as gravitons. However, these have still not been detected as yet.

Electromagnetic force – virtual photons

The boson which carries electromagnetic force between charged particles is known as the virtual photon. Particles which consist of an electric charge are able to repel or attract one another by the exchange of these bosons.

Strong nuclear force – gluons

The exchange particles which are involved in strong nuclear force attraction are known as gluons.

Weak nuclear force – W+ and W- bosons

Exchange particles which are involved in weak nuclear force interaction are known as W and Z bosons. However, for your exam you only need to be aware of W+ and W- bosons. Quarks and leptons place forces on one another by the exchange of these bosons. However, this force is very weak and can only act over very short distances.

Feynman diagrams

It is possible to visually represent particle interactions through Feynman diagrams. They also show which exchange particles are involved.

Repulsion between electrons (e^–):

A photon (p) and an electron (e-) combining to create a neutron (n) and a neutrino (?):

[INSERT DIAGRAM]

?- decay:

?+ decay:

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Electron capture:

[INSERT DIAGRAM]

Neutrino-neutron collisions:

[INSERT DIAGRAM]

Anti-neutrino-proton collisions:

[INSERT DIAGRAM]

Electron-proton collisions:

[INSERT DIAGRAM]