Final answer:
A change in a substance that does not involve a change in the chemical composition of that substance is known as a physical change. This includes alterations to the physical properties like density or color, but does not result in forming a new substance.
Step-by-step explanation:
An alteration in the form of properties of a substance without changing the chemical nature of the substance or forming a new substance is called a physical change. This involves changes in physical properties, which are characteristics of matter that do not change its chemical composition. For example, when ice melts into water, it undergoes a physical change; the water is still H₂O, but the form has changed from solid to liquid. Similarly, when you hammer gold into foil, its shape changes, but it remains chemically gold. Physical changes may include changes in state, shape, texture, or other physical attributes. Physical properties such as density, color, a substance's melting or boiling point, and electrical conductivity are examples that show how a substance can be characterized without altering its chemical structure. In contrast, chemical properties describe a substance's ability to form new substances through chemical changes, such as iron rusting to form a new compound, iron oxide.