Which of the following is an example of a composite material?

Composite materials are characterized by being made from two or more constituent materials that exhibit different physical or chemical properties, which remain separate and distinct within the finished structure. This results in a material with enhanced properties compared to the individual components.

In the case of glass fiber reinforced polymer, it combines glass fibers, which provide strength and rigidity, with a polymer matrix that contributes to light weight and resistance to corrosion. The synergy between these materials allows the composite to achieve superior performance characteristics such as added strength, reduced weight, and improved durability. This unique combination is what clearly identifies it as a composite material.

Pine wood, while a natural composite in terms of structure (made from cellulose fibers in a lignin matrix), is generally not classified as a composite material in engineering terms, as it does not derive its benefits from a designed combination of distinct materials. Copper and steel are individual elements and alloys respectively, which do not involve the combination of different materials to create enhanced properties; thus, they do not fit the definition of composite materials.