Point particle of point charges cannot be maintained in an equilibrium configuration solely by the electrostatic interaction of the charges. In quantum mechanics, there is a distinction between an elementary particle (also called "point particle") and a composite particle. An elementary particle, such as an electron, quark, or photon, is a particle with no internal structure. Whereas a composite particle, such as a proton or neutron, has an internal structure (see figure). However, neither elementary nor composite particles are spatially localized, because of the Heisenberg uncertainty principle. The particle wavepacket always occupies a nonzero volume. For example, see atomic orbital: The electron
Cassidy (given name) Cassidy (given name) Cassidy is a given name derived from an Irish surname and ultimately from the Gaelic given name "Caiside", meaning "clever" or "curly-haired." The name "Caiside" comes from the Gaelic word element "cas", according to "Behindthename.com" Cassidy was the 244th most popular name for girls born in the United States in 2009. It was most popular in 1999, when it was the 99th most popular name for American girls. It first appeared among the 1,000 most popular names for American girls in 1981. Kassidy, an alternate spelling, was ranked as the 443rd most popular name for girls in