Breaking glass is considered a physical change because it alters the form of the glass without changing its chemical composition. When glass is broken, it shatters into smaller pieces, but the material itself remains the same—silicon dioxide (SiO2), which means that the properties of the glass, including its chemical identity, remain unchanged.
In contrast, a chemical change would involve a substance transforming into a different substance altogether, typically resulting in changes to its molecular structure. For example, if glass was melted down and combined with other materials to create a new product, that would be a chemical change. However, simply breaking the glass does not create any new materials; it just changes the shape and size.
Thus, the act of breaking glass demonstrates a physical alteration where the original material can still be recognized, which is why it is classified as a physical change.