Composite particle facts for kids
Composite particles are subatomic particles that are made of more than one quark. Simple particles like protons are actually composites of multiple quarks. Protons are known as baryons, which means that they are made of exactly three quarks. Baryons are in a family called Hadrons, which simply means that they are made of quarks. The only other subcategory of Hadrons is Mesons, which are made of one quark and one antiquark.
Since they are made of quarks, composite particles are not so much hard balls, but rather like clouds that contain these quarks. Depending on the energy contained by the quarks, the quarks of a proton vibrate, and this gives a proton a size larger than the actual size of the three quarks combined.
en:List of particles#Composite particles
Composite particle Facts for Kids. Kiddle Encyclopedia.