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 that we've observed take place in the universe, they can be broken down to be described by only four (well, generally four - more on that later) types of interactions:
- Gravity
- Electromagnetism
- Weak Interaction (or Weak Nuclear Force)
- Strong Interaction (or Strong Nuclear Force)
Gravity
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.
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.
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 & 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.
(kaynak: http://physics.about.com)
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