Let's take a closer look at the force that keeps the quarks together.
Particle physicists explain all the forces as force carrier particles (bosons)
that are exchanged by matter building particles (fermions). On this website it's easy
to tell the two fundamentally different kinds of particles apart. Fermions are illustrated
as circles while bosons look like little suns.
Quarks are matter building particles. They exchange particles called gluons. The force created
by the exchange of gluons between quarks is the color force.
Particles that take part in the color interaction have to be color charged. This is similar to the
electrically charged particles. In contrary to electrically charged particles, which can
only be charged (+) or anticharged (-), there are three color charges (red, green and blue)
and three anti-color charges (anti-red, anti-green, and anti-blue).
Of course, these colors don't have anything
to do with the colors we know, but they are a good way of illustrating some properties of the color charge.
The quarks keep exchanging gluons. Whenever they
exchange a gluon, they exchange their color charge. You can imagine it as in the picture on the
right. A quark that starts off with a blue charge may be green the next moment and then turn
red. This is different from the electric charge: an electrically charged particle always keeps
the same charge (an electron will always have the charge -1)
while color charged particles exchange their color.
Like quarks, gluons have a color charge. They, however, always carry a color and an anticolor
with them. In the animation on the left you can see a simple animation of how two down quarks exchange a gluon
with the color charge blue anti-green. Color charge is conserved .
Take a look at the still picture and check whether there is always the same amount of each color. Tip:
when you have an anti-color you have to subtract it.