Youngs modulus

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Young's modulus [for Thomas Young], number representing (in pounds per square inch or dynes per square centimeter) the ratio of stress to strain for a wire or bar of a given substance. According to Hooke's law the strain is proportional to stress, and therefore the ratio of the two is a constant that is commonly used to indicate the elasticity of the substance. Young's modulus is the elastic modulus for tension, or tensile stress, and is the force per unit cross section of the material divided by the fractional increase in length resulting from the stretching of a standard rod or wire of the material. See strength of materials.

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Young's modulus (E) The ratio of longitudinal stress σ (force F divided by area A, i.e. σ = F/A) to longitudinal strain (change in length δL divided by original length L, i.e. δL/L) in the presence of lateral strain: E = (F/A)/(δL/L). If there were no lateral strain, Young's modulus would be equal to the axial modulus.