A physical change is a change in which no new substances are formed. Physical changes affect the form of a chemical substance, but not its chemical composition. Mixtures can be separated into their parts by physical methods, such as spinning in a centrifuge. but can not usually be used to separate compounds into chemical elements or simpler compounds.
Most physical changes are reversible and their mass does not change. Some examples are changes of shape, changes of states, and passing electricity through a copper wire. Some physical changes are melting, freezing and boiling.
Many physical changes also involve the rearrangement of atoms most noticeably in the formation of crystals. Many chemical changes are irreversible, and many physical changes are reversible, but reversibility is not a certain criterion for classification. Although chemical changes may be recognized by an indication such as odor, color change, or production of a gas, every one of these indicators can result from physical change.