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Stiffness

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	Stiffness
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	Topics Stiffness Topic Home Stiffness is the resistance of an elasticFacts About Elasticity (physics) Elasticity is a branch of physics which studies the properties of elastic materials.... body to deflectionDeflection [[fr:Flexion ]... or deformationDeformation In engineering mechanics, deformation is a change in shape due to an applied force.... by an applied forceForce In physics, force is that which changes or tends to change the state of rest or motion of a body.... . It is an extensive material propertyIntensive and extensive properties In physics and chemistry an intensive property of a system is a physical property of the system that does not depend on the ... . Definition The stiffness, k, of a body is where P is the applied force δ is the deflected distance In the International System of UnitsInternational System of Units The International System of Units is the modern form of the metric system.... , stiffness is typically measured in newtonNewton The newton is the SI unit of force.... s per metreMetre The metre, or meter , is a measure of length.... . As both the applied force and deflectionDeflection [[fr:Flexion ]... are vectorVector (spatial) Overview In physics and in vector calculus, a spatial vector, or simply vector, is a concept characterized by a magnitude and a... s (respectively P and δ), in general their relationship is characterised by a stiffness matrix, k, where: The deflection can, in general, refer to a point distinct from that where the force is applied and a complicated structure will not deflect purely in the same direction as an applied force. The stiffness matrix enables such systems to be characterised in straightforward terms. The inverseInverse Inverse or Inversion may refer to:... of stiffness is complianceFacts About Compliance Compliance can mean:In mechanical science and physiology, the reciprocal of elastance... , typically measured in units of metres per newton. In rheology it may be defined as the ratio of strain to stress , and so take the units of reciprocal stress, e.g. 1/PaPascal (unit) The pascal* is the SI derived unit of pressure or stress .... . Rotational stiffness A body may also have a rotational stiffness, k, given by where M is the applied momentMoment (physics) In physics, the moment of force is a quantity that represents the magnitude of force applied to a rotational system at a dis... θ is the rotation In the SI system, rotational stiffness is typically measured in newton-metres per radianRadian Overview The radian is a unit of plane angle.... . In the SAE system, rotational stiffness is typically measured in inchInch An inch is the name of a unit of length in a number of different systems, including English units, Imperial units, and Unit... -poundPound-force A pound-force is a unit of force. One pound-force is the force equivalent to that exerted on a mass of one avoirdupois pound... s per degreeDegree (angle) A degree, usually symbolized ', is a measurement of plane angle, representing 1/360 of a full rotation.... . Further measures of stiffness are derived on a similar basis, including: shear stiffness - ratio of applied shearShear stress In physics, shear stress is a stress state in which the shape of a material tends to change without particular volume change... force to shear deformation torsional stiffness - ratio of applied torsionTorsion (mechanics) In solid mechanics, torsion is the twisting of an object due to an applied torque.... moment to angle of twist Relationship to elasticity In general, elastic modulusElastic modulus An elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance's tendency to ... is not the same as stiffness. Elastic modulus is a property of the constituent material; stiffness is a property of a solid body. That is, the modulus is an intensive propertyIntensive and extensive properties In physics and chemistry an intensive property of a system is a physical property of the system that does not depend on the ... of the material; stiffness, on the other hand, is an extensive propertyIntensive and extensive properties In physics and chemistry an intensive property of a system is a physical property of the system that does not depend on the ... of the solid body dependent on the material and the shape and boundary conditions. For example, for an element in tensionTension (mechanics) Tension is a reaction force applied by a stretched string on the objects which stretch it.... or compressionPhysical compression Physical compression is the result of the subjection of a material to compressive stress, resulting in reduction of volume.... , the axial stiffness is where A is the cross-sectional area, E is the Young's modulusYoung's modulus In solid mechanics, Young's Modulus is a measure of the stiffness of a given material.... , L is the length of the element. For the special case of unconstrained uniaxial tension or compression, Young's modulus of elasticityYoung's modulus In solid mechanics, Young's Modulus is a measure of the stiffness of a given material.... can be thought of as a measure of the stiffness of a material. Use in engineering The stiffness of a structure is of principal importance in many engineering applications, so the modulus of elasticity is often one of the primary properties considered when selecting a material. A high modulus of elasticity is sought when deflectionsDeflection [[fr:Flexion ]... are undesirable, while a low modulus of elasticity is required when flexibility is needed. See also ElasticityElasticity (physics) Elasticity is a branch of physics which studies the properties of elastic materials.... Elastic modulusElastic modulus An elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance's tendency to ... HardnessHardness In materials science, hardness is the characteristic of a solid material expressing its resistance to permanent deformation.... Moment of inertiaMoment of inertia Moment of inertia, also called mass moment of inertia and, sometimes, the angular mass, quantifies the rotationa... Young's modulusYoung's modulus In solid mechanics, Young's Modulus is a measure of the stiffness of a given material.... Hooke's lawHooke's law In physics, Hooke's law of elasticity is an approximation which states that the amount by which a material body is deformed ...