A composite is a combination of two or more different materials. The new material combines the best properties, such as strength and lightness, of each of the individual materials. There are examples of composites all around us. Boats, bikes, tennis rackets, even dental fillings are all made of composites. Most composites are synthetic materials, but they also occur in nature.
Bone is a composite of hydroxyapatite and a protein called collagen. The hydroxyapatite is a brittle but hard and rigid material that gives bone its structural strength. The collagen is soft and spongy, giving bone its flexibility. Bone is 80–90 per cent hydroxyapatite and 10–20 per cent collagen protein.
The Smart car is a modern two-seater car that is very light, so it uses less fuel than heavier cars. It has also been designed to take up less room in city centres. Over 40 per cent of a Smart car is made from composite materials. It has been put together in panels, so each composite panel can be easily replaced.