I have been writing about quarks a lot so now I would like to shortly summarize what they are.
Quarks have been discovered when scientists saw that paths of particles traveling close to neutron are distorted by some weak electromagnetic field. Then they discovered that neutron is neutral but it contains particles which are not neutral: quarks.
If I told you that protons and neutrons are only made up of three up and down quarks you could easily figure out what is inside them. Proton´s charge is +1 which means there has to be 2 ups and 1 down because UP(charge)=+2/3 DOWN(charge)=-1/3 === 2*2/3+(-1/3)=+1. While neutron is made up of two downs and one up which equals to 0.
As you can see from the table there are six types (flavors) of quarks. I talked only about two of them because they are much more common then charm, strange, top and bottom. The reason why those four are less common is that they are extremely heavy compared to up and down quarks and they will decay into up and downs. Up and downs can not decay to anything which makes them stable. Even then it is thought that proton (uud) can decay.. I talked about it earlier so you can check my other posts.
Flavor is one attribute but there is another. I mentioned it in post about strong interaction and it is color of quarks. There are three “colors”: RGB — red, green and blue and antired, antigreen and antiblue. Those colors always have to add up to white color. There are lot of combinations which can do this – RGB, antiRantiGantiB, blue and antiblue, red and anti red… and many others
It would be far too easy without gluons which are holding quarks together.
They are usually drawed as a short string between quarks. The thing that they do is color changing. They do it at two points: when they enter and when they leave quark.
There is hypothetical astronomical object called Quark star which should be made up of free quarks. Also it is thought that right after big bang there was state of matter in the Universe called quark-gluon plasma… soup of free quarks and gluons. We are not yet able to create this because it probably needs extremely high temperatures.
On the left is a picture which compares mass of quarks. On the botom you can see grey proton and really small, red electron. Top quark is the largest one.
Particles which are made up of quarks are sorted into different groups: mesons and baryons you can see on the picture what they can look like and how colors add up to white.