Gravitational, electromagnetic, and nuclear forces?

Question

1. Why are these forces often called fundamental or basic forces?
2. Where are these forces found?
3. How are other forces related to them?

Answer 1

Actually, scientists have already unified the electromagnetic force and the "weak" nuclear force, when they came up with "electroweak theory".

But if we ignore that, then the answer to question 1 is:

Virtual photon particles carry the electromagnetic force,
gluon particles carry the strong nuclear force,
virtual W-,W+,and Z particles carry the weak nuclear force,
and we imagine that graviton particles carry the gravitational force. Each force has different fundamental particles acting as the force carriers.

Question 2: Atomic nuclei are held together by the strong nuclear force, electrons are held in atoms by the electromagnetic force, certain nuclear decays are evidence of the weak nuclear force, and then of course there's gravity.

Question 3: Most of what we think of as "forces" in our daily lives are actually due to the electromagnetic force: collisions, friction, string tension, gas pressure, etc. The electromagnetic force causes atoms to repel (such as a ball bouncing on the ground) and to stick (as in friction and viscosity, and in molecular bonds, etc.).

Answer 2

They are "fundamental" because as of yet, we have not been able to simplify force past these three for the most part. there have been theories which unify the electromagnetic force and the nuclear forces, but gravitational force seems to be the odd one out. they each act in their own energy range so to say, gravitation being over large distances and large masses accumulated from smaller ones (think sun, galaxy, moon, jupiter etc...). Electromagnetic forces act on somewhat smaller scales, although the range varies widely from planetary interactions in the magnetosphere to atoms with electrons and protons. nuclear forces are the forces which hold the nucleus(strong) and the individual subatomic particles together(weak).

all other forces can be said to be a combination of these three basic types of force. for instance, standing on the ground is a combination of the electromagnetic forces and nuclear forces between the ground and your feet resisting eachother, and thus repulsing eachother, while overcoming the force of gravity which pulls them together. thrust from a rocket engine is a combination of electromagnetic interactions between atoms and molecules which releases energy and makes the atoms move considerably faster, thus pushing off of eachother and what ever they are contained in, and providing a force in the direction opposite of their travel. all forces can be broken down this way into components of each of the "fundamental" forces.

who knows though, one day we might find a new force, or one day we might find a way to express all these forces as part of one greater overlaping force. only time will tell! hope this helps :)