Glossary
physical change
A physical change alters a substance's form, size or state without making a new substance — melting, cutting and dissolving are the usual examples.
A physical change alters how a substance looks or what state it is in without turning it into something else. Ice melting, sugar dissolving in water, glass shattering and a wire being bent are all physical changes: the material is the same material afterward, only rearranged. The test is composition, not appearance — melt wax and it is still wax, freeze it and it is wax again, which is why most physical changes can be reversed by taking away or adding the energy that caused them. Dissolving is the case that trips people: the sugar is not gone and has not reacted, it is dispersed among water molecules, and boiling the water off returns it. A question that shows a change and asks whether it is physical is asking whether anything new was made. If the answer is nothing new, the change was physical.
Taught in
Related terms
- matter — Matter is anything with mass that takes up space, and it exists as a solid, a liquid, a gas or a plasma.
- chemical change — A chemical change makes a new substance with new properties — burning, rusting and digesting food are chemical changes.
Source: NIST periodic table and reference data for the atomic masses and half-life figures, NIH PubChem for the substance data, and NIST Special Publication 811 for the unit conventions — the same sources the chemistry guide cites. All three are US federal government material, not subject to copyright in the United States. Every definition, example and calculation above was written for this course; no dictionary or textbook text is reproduced. (NIST and PubChem accessed 2026-10-26; definitions written 2026-10-27)