Quark is the tiniest particle making up every living matter on Earth. It’s responsible for the composition of several other composite elements, such as protons and neutrons. In other words, molecules are made of atoms, atoms consist of neutrons and protons, and neutrons and protons are made of quarks. Prior to the discovery of quarks, atoms were considered the smallest particles.

A quark is extremely smaller than proton – almost 2,000 times smaller than the radius of a proton. A quark’s size is so small it’s not possible to view the particle through any man-made instrument, including a microscope. Measuring a quark is therefore out of the picture. Quarks are stuck to each other by a tiny substance or particle called gluon. This means though quarks are extremely tiny, they could possibly be made of even tinier particles.  

Classification

Quarks can be categorized as: up, strange, down, bottom, charm, and top. They are usually referred to in pairs – up/down, top/bottom, and charm/strange. These types are commonly referred to as flavors, wherein the ‘up’ and ‘down’ quarks are the lightest of them all. The up and down quarks are most stable and make up every visible, normal particle on the planet. Every proton has two up quarks and one down quark; and a neutron is made of two down quarks and a single up quark.

The other four flavors are generally part of intense collisions involving high-energy particles – such as cosmic rays, radio waves, etc. A quark doesn’t stay the same throughout. This means ‘down’ quarks could easily become ‘up’ quarks, and ‘strange’ quarks could transform into ‘charm’ quarks.

Properties

Quarks have several intrinsic traits such as mass, electric charge, spin (rotation) and color charge. The charm, top and up quarks have a +2/3 positive charge, whereas the strange, down and bottom quarks have a -1/3 negative charge. Though the strange and down quark have the same charge, the strange quark is heavier. The heaviest of the three is the bottom quark. Similarly, ‘charm’ is heavier than ‘up’, with ‘top’ being the heftiest.

When quarks interact, they tend to exchange gluons, which could cause the quarks’ colors to change. The color force is strongest when quarks move away from each other, and it’s the weakest when quarks come close to each other. A quark is strongly influenced by color force, which is why quarks are usually attached to each other.