Grade 11 elasticity
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Transcript of Grade 11 elasticity
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ELASTICITYPhysics Grade XI2016
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Aim of this lessonExplain the effect of the force to the elasticity character and vibration
Sub Chaptera. Elasticityb. Simple Harmonic Motion
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Elasticity• the ability of an object or material to resume its normal
shape after being stretched or compressed
Inelasticity ?
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Stress, Strain and Modulus of Elasticity
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Stress• Stress is "force per unit area" - the ratio of applied force F
to cross section area - defined as "force per area".
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• tensile stress - stress that tends to stretch or lengthen the material - acts normal to the stressed area
• compressive stress - stress that tends to compress or shorten the material - acts normal to the stressed area
• shearing stress - stress that tends to shear the material - acts in plane to the stressed area at right-angles to compressive or tensile stress
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• Tensile or compressive stress normal to the plane is usually denoted "normal stress" or "direct stress" and can be expressed as
• σ = Fn / A (1)• where• σ = normal stress ((Pa) N/m2)• Fn = normal component force (N)• A = area (m2)
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Example• A force of 10 kN is acting on a circular rod with diameter
10 mm. The stress in the rod can be calculated as• σ = (10 x103 N) / (π ((10 x10-3 m) / 2)2)• = 127388535 (N/m2) • = 127 (MPa)
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Strain• Strain is defined as "deformation of a solid due to stress"
and can be expressed as
whereΔL = change of length (m)L = initial length (m)ε = strain - unitless
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Cyberphysics.co.uk
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Modulus of ElasticityE = Young's modulus (Modulus of Elasticity) (N/m2 (Pa)
Young's modulus can be used to predict the elongation or compression of an object.
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• Elasticity Constant
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Hooke’s LawHooke's law is a principle of physics that states that the force F needed to extend or compress a spring by some distance X is proportional to that distance.
where k is a constant factor characteristic of the spring X is small compared to the total possible deformation of the spring.
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Example
Calculate the value of spring constant !
F = k Δx40 N = k (0.08 m)K = 500 N/m
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SWTextbook “Exercise”Page 96Page 98Page 100
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Simple Harmonic Motion
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𝒂=𝒌𝑨𝒎 𝐜𝐨𝐬 (𝝎𝒕+𝜽𝟎)
𝑇=2𝜋 √ 𝑙𝑔
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Hooke’s Law for the composition
Series
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Parallel
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Give us SW please....