There are four fundamental forces in nature: the strong force (which is the joining force between quarks and atomic nuclei), the weak force (which causes radioactive decay), the electromagnetic force (which keeps the atoms together) and the gravitational force (which acts on any object with energy or mass in the universe). Leptons are subject to all these fundamental forces except for the strong force. The reason behind this exception is that the strong force has a very short range, even shorter than that of an atomic nucleus, which is the reason why the strong force is limited to that area.
Quarks were named by Murray Gell-Mann, a Nobel Prize winner, after a word in James Joyce's book 'Finnegan’s Wake'. Quarks have fractional charge, which is the reason why they are not able to exist freely as per a fundamental force called ‘strong force’. Mediated by force-carrying particles called gluons, the strong force keeps quarks attracted to one another and acts within the nucleus of an atom.
As quarks move apart, the force between them increases; however, some quarks are never detected. The field of study which concerns itself with the interactions between quarks and gluons is known as Quantum Chromo Dynamics (QCD). Quarks are subject to all the fundamental forces which are mentioned above.