A physicist's study involves the study of ENERGY, antimatter, ions, MATTER, and atoms. ENERGY is a form of power that can be used to do work, such as heat, light, or motion. Antimatter is a type of MATTER composed of particles with the same mass as regular MATTER but with opposite charges. Ions are atoms or molecules that have gained or lost one or more electrons, giving them a net positive or negative charge. MATTER is anything that has mass and occupies space. Atoms are the smallest particles of an element that still retain the properties of that element.