Particles

Particles (or corpuscles) are the smallest units of matter. They are the building blocks of all larger objects in the universe, including planets, stars, and galaxies. Particles come in a variety of sizes and shapes, and they interact with each other in different ways. The behavior of particles is governed by the laws of physics.

The term “particle” can refer to either a physical object or an abstract concept. Physical particles include atoms, molecules, electrons, protons, and neutrons. Abstract particles include quarks and leptons. All particles have mass and occupy space. Some particles also have electric charge.

Atoms are the simplest type of particle; they are composed of only one kind of element (e.g., hydrogen or gold). Molecules are made up of two or more atoms bonded together (e.g., water or DNA). Electrons orbit the nucleus of an atom; they have negative charge and very little mass compared to protons and neutrons. Protons reside in the nucleus along with neutrons; they have positive charge and slightly more mass than electrons. Neutrons do not have electric charge; their mass is similar to that of protons. Quarks make up protons and neutrons; there are six types (or “flavors”) of quarks: up, down, strange, charm, bottom, and top. Leptons include electrons as well as muons and taus (heavier cousins of the electron); there are also three types of neutrinos associated with leptons.

All known interactions between particles can be explained by four fundamental forces: gravity, electromagnetism, strong nuclear force, and weak nuclear force. Gravity is attractive force that exists between any two masses; it is responsible for holding together objects like planets and stars as well as providing structure for galaxies . Electromagnetism is another attractive force that occurs between electrically charged particles; it holds atoms together in molecules as well as determines how light interacts with matter . The strong nuclear force binds together quarks inside nuclei despite their mutual repulsion due to electrical charges ; this same force also holdsprotonsandneutronstogetherinsideatomicnuclei . Theweaknuclearforceisresponsibleforthedecayofradioactiveelements ;itisthe weakestofthefourfundamentalforces ,butitsrangeispracticallyunlimited .
While all four forces are important for understanding how our universe works , physicists often focus on studying either gravity or electromagnetism because these two forces play dominant roles at different size scales . For example , gravity governs the motionsofplanetsandstars while electromagnetismdeterminesthelight emittedbytheseobjectsaswellastheirinteractionswithoneanother . Incontrast , thenuclearforcesarerelativelyweakcomparedtogravityandemagetoonlyactat extremely small length scales suchasthoseassociatedwith atomic nuclei .