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OCR AS Physics A Key terms
Stiffness is the resistance of a material to deformation. The stiffer a material is the less it will
stretch for a given force.
Elastic and plastic
A material is said to be elastic if it returns to its original shape and size when the force is
removed. Conversely, a material is said to be plastic if it does not return to its original
Most materials are elastic up to a point, known as their elastic limit. Beyond this point they
A material is ductile if it can be shaped without breaking. A ductile material will undergo
deformation before breaking.
A material is said to be hard if it cannot easily be scratched or damaged.
A material is brittle if it fractures when under stress with little or no deformation, for
example glass when dropped onto the floor shatters as it is brittle. Brittle materials
obey Hooke's law until they snap. A stress-strain graph of a brittle material is therefore just a
Toughness descirbes how well a material resists fracturing when under stress. It is the area
under a stress-strain graph.
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Stress is a measurment of strength, it is how much pressure a material can withstand
without undergoing physical change. There are a number of different types of stress.
Tensile strength/fracture stress
Tensile strength or fracture stress is the amount of stress a material can be put under
before it fractures.
Yeild stress and yeild stength
Yeild stress or yeild strength is the amount of stress a material can take before it deforms
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You need to be able to use and recognise the parts of a graph of stress plotted against
The first thing to know is that the area under the curve represents the toughness of the
material - how much it resists stress.
Between the origin and point A the material is said to be elastic - the ratio between stress
and strain is constant, obeying Hooke's law. In this region the material will return to it's
original size.…read more