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UNIT 1 Mechanics and Materials (Definitions)
Breaking stress The maximum stress (force per unit area that can be applied to a material
before it is pulled apart (also called the tensile strength).
Brittle A material that shows no plastic deformation just beyond its elastic limit.
Centre of gravity The point through which all the weight of an object appears to act.
Compressive strain The amount of deformation per unit length of a material.
Compressive stress The compressive force per unit area.
Density Mass per unit volume (p=m/V)
Ductile A material that shows plastic deformation before failure under tension. A ductile
material can be pulled into wires, or threads. E.g. Copper.
Elastic limit The load on a spring beyond which the extension increases more rapidly than
expected, and the spring remains permanently deformed when the load is removed.
Hard Materials that resist plastic deformation by surface indentation or scratching. E.g.
Laminar flow Smooth fluid flow in which parallel layers have a constant velocity.
Limit of proportionality Stress is proportional to strain up to this point .
Malleable Materials that show a large plastic deformation under compression. These materials
can be beaten into sheets. E.g. Gold
Stiff Gradient of a forceextension graph. High Young modulus. E.g. steel.
Stiffness A measure of the resistance of a material to deformation by tensile force.
Streamline flow Lines of laminar fluid flow. At any point on the streamline the velocity of the
fluid will be constant over time.
Strength The ability of a material to withstand stress.
Tensile strain The extension per unit length of a material subjected to a tensile force.
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Tensile stress The tensile force per unit area.
Terminal velocity Constant velocity of a falling object in which the force of gravity downwards
is balanced by the drag force.
Tough Materials that are able to withstand impact forces without breaking and require a large
force to produce a small plastic deformation. E.g. mild steel, copper, rubber tyres.
Turbulent flow Irregular chaotic flow in which eddies form. The fluid velocity is not constant
over time.…read more