The Four Fundamental Forces.
In Physics, the fundamental forces describe how particles interact with one another. The four known forces are the Strong Nuclear Force, the Weak Nuclear Force, Electromagnetism and Gravitation. These forces are considered fundamental because they cannot be explained in terms of any other force. The quest to bring together the four forces into a single entity (a TOE - Theory of Everything) is the pursuit of many physicists, but so far has proven to be a challenging task, which even eluded Einstein himself!
Strong Nuclear Force
Strength: 1 (All strenghts to follow are relative to this one.) Range: 10-15 m
The Strong Nuclear Force, aptly named because it is the strongest of the four forces, is responsible for everything that we know today. This force holds together the protons and neutrons together in the atomic nucleus despite the particles’ urge to repel each other. The mediators of the Strong Nuclear Force are particles called Gluons, which also hold quarks together to form particles such as the proton.
Strength: 1⁄137 Range: Infinite
The Electromagnetic force is responsible for, as you can probably tell, electricity and magnetism. This force is mediated by Photons, massless particles that are the basic unit of light. You probably know that opposite charges attract, and like charges repel - this is a direct result of the Electromagnetic force. When a particle attract or repels another particle, what actually happens is that photons are exchanged, and the release or absorption of the photon’s energy causes the particle to come closer or dart away. This force is responsible for many everyday, observable occurrences. The Electromagnetic force is why your computer isn’t falling right through your desk right now; because the atoms in your computer and in the desk resist being displaced from the exchange of photons.
Weak Nuclear Force
Strength: 10-6 m Range: 10-18 m
The Weak Nuclear Force is the most unfamiliar to us in our everyday lives. However, it is the force that is responsible for radioactive decay and hydrogen fusion in stars. The mediators of this force are the massive W and Z bosons. This force is also capable of changing the flavor of a quark, i.e. changing one type of quark into another.
Strength: 6 * 10-39 m Range: Infinite
Gravity, of course, is the most familiar of all the fundamental forces. However, is it also the least likely to compromise, as it has proven extremely difficult to associate gravity into the other forces into a Theory of Everything. In fact, the modern model of the Universe, the Standard Model, does not even include gravity because of this! In short, Gravity is a force by which physical bodies attract each other. In more precise terms, Gravity is an inverse square law with incorporates the masses of two bodies, the gravitational constant, (6.67300 × 10-11 m3 kg-1 s-2,) and the distance separating the bodies. Gravity is most observable by providing weight to objects and what causes objects to fall to the ground when dropped. Gravity also causes coalesced matter to remain intact, thus accounting for most of the macroscopic objects in the Universe. Every object exerts a gravitational force on every other object, although the force becomes extremely weak at large distances.
To show the weakness of Gravity compared with the other forces, consider this. After running a comb through your hair several times, place it close to a flat piece of paper. If done correctly, the paper should lift up and touch the comb. An entire planet’s gravity was required to keep that piece of paper down, but a simple comb with a few charged particles was able to pick it up!