Steel
cables over 1 m in diameter support a suspension bridge.
The load of the bridge causes a tensile force in the
cable, setting up a tensile
stress. This has the effect of stretching the cable, setting up a tensile strain.
In addition to the cable being elastic
and strong, it must be stiff.
The material property (constant) which tells us how stiff it is within its elastic
limit is called the Young Modulus, E,
where:
Unit: N m-2.
An elastic material returns to its original length (or shape) when any
load is removed.
A plastic material distorts easily but does not break.
A strong material is one with a high breaking stress - i.e. a high
tensile stress is needed to break it.
A weak material is one with a low breaking stress.
A stiff material needs a large force (tensile stress) to produce a
small extension (tensile strain) - it is difficult to change its shape.
A flexible material only needs a small stress to produce a large
extension - it is not difficult to change its shape.
