What is a particle in physics?

Answer 1

A body whose spatial extent and internal motion and structure, if any, are irrelevant in a specific problem.

This is why, for certain problems, dust 'particles' can be considered (for brownian motion experiments, for example). In other cases (like cathode-ray tubes) a negative beam of particles is launched (these are electrons). In experiments of neutron diffraction, neutrons can be considered to be particles because their interaction with matter is always the same. The internal structure of the neutron gives it a magnetic moment, but as all neutrons posess the same internal structure they can be considered as particles.

Water molecules can be considered particles when in liquid (and gaseous) state because their internal structure has no effect on their behaviour. When water freezes, the isotope of hydrogen (and oxygen, to a lesser extent) drastically alters how the ice crystals form. For this reason, water molecules in a freezing experiment can't be considered particles.

Answer 2

in physics there are actually several kinds of particles. First are the Elementary, or fundamental particles. These are particles not known to have substructure, like quarks, muons, gluons, photons, etc...These Elementary particles can also be referred to as point particles, which you will hear sometimes...Second type is a composite particle...these are the more familiar ones, like Hydrogen and Oxygen...

Answer 3

a particle in physics is a sub division of another particle and so on. There is always a particle after discovering one there remains another.