Students should be able to recall some examples of composites.

The idea

A composite combines two or more materials so that the useful properties of each are retained in the finished article. One material, often called the reinforcement, provides strength or stiffness; the other, the matrix, holds the reinforcement in place and spreads any load. Fibreglass is glass fibres set in a polymer resin: the fibres give tensile strength while the resin binds them and resists impact. Carbon fibre composites use carbon fibres in a resin matrix and are valued where low mass and high strength matter, such as bicycle frames and aircraft parts. Reinforced concrete embeds steel rods in concrete, combining concrete's compressive strength with steel's tensile strength. Wood and bone are natural composites. To recall examples, link each named composite to its two components and one use.

What earns the marks

• Names at least two composites, such as fibreglass, carbon fibre composite or reinforced concrete.
• Identifies the two components of a named composite, for example glass fibres and a polymer resin in fibreglass.
• States that the reinforcement provides strength or stiffness while the matrix binds the materials together.
• Links a named composite to a use that depends on its combined properties, such as reinforced concrete in building foundations.
• Recognises that a composite is not a simple mixture or alloy but a material whose components keep distinct roles.

Common mistakes and how to put them right

• Treating any mixture as a composite.

  Put it right: A composite has a reinforcement held in a matrix with a structural purpose.

• Naming only one component, such as saying fibreglass is glass.

  Put it right: Name both the glass fibres and the polymer resin.

• Confusing composites with alloys.

  Put it right: Alloys are mixtures of metals, whereas composites combine materials such as fibres and resins.

Exam tips

• Learn two composites in detail, naming both components and one use for each, so a recall question can be answered quickly.
• When asked for examples, give the composite name rather than only its components, for example reinforced concrete rather than steel and concrete.
• Use the words reinforcement and matrix to show understanding of why the components are combined.