What is "young's modulus"

Modulus \Mod"u*lus\, n.; pl. Moduli. [L., a small measure. See Module, n.] (Math., Mech., & Physics) A quantity or coefficient, or constant, which expresses the measure of some specified force, property, or quality, as of elasticity, strength, efficiency, etc.; a parameter. Modulus of a machine, a formula expressing the work which a given machine can perform under the conditions involved in its construction; the relation between the work done upon a machine by the moving power, and that yielded at the working points, either constantly, if its motion be uniform, or in the interval of time which it occupies in passing from any given velocity to the same velocity again, if its motion be variable; -- called also the efficiency of the machine. --Mosley. --Rankine. Modulus of a system of logarithms (Math.), a number by which all the Napierian logarithms must be multiplied to obtain the logarithms in another system. Modulus of elasticity.

1. The measure of the elastic force of any substance, expressed by the ratio of a stress on a given unit of the substance to the accompanying distortion, or strain.

2. An expression of the force (usually in terms of the height in feet or weight in pounds of a column of the same body) which would be necessary to elongate a prismatic body of a transverse section equal to a given unit, as a square inch or foot, to double, or to compress it to half, its original length, were that degree of elongation or compression possible, or within the limits of elasticity; -- called also Young's modulus.

   Modulus of rupture, the measure of the force necessary to break a given substance across, as a beam, expressed by eighteen times the load which is required to break a bar of one inch square, supported flatwise at two points one foot apart, and loaded in the middle between the points of support.
   --Rankine.

Young's modulus, which is also known as the elastic modulus, is a mechanical property of linear elastic solid materials. It defines the relationship between stress (force per unit area) and strain (proportional deformation) in a material. Young's modulus is named after the 19th-century British scientist Thomas Young. However, the concept was developed in 1727 by Leonhard Euler, and the first experiments that used the concept of Young's modulus in its current form were performed by the Italian scientist Giordano Riccati in 1782, pre-dating Young's work by 25 years. The term modulus is the diminutive of the Latin term modus which means measure.

A solid body deforms when a load is applied to it. If the material is elastic, the body returns to its original shape after the load is removed. The material is linear if the ratio of load to deformation remains constant during the loading process. Not many materials are linear and elastic beyond a small amount of deformation. A constant Young's modulus applies only to linear elastic materials. A perfectly rigid material has an infinite Young's modulus because an infinite force is needed to deform such a material. A material whose Young's modulus is very high can be approximated as rigid.

A stiff material needs more force to deform compared to a soft material. The Young's modulus is a measure of the stiffness of a solid material.

Do not confuse:

• stiffness with strength: the strength of material is the amount of force it can withstand and still recover its original shape;
• material stiffness with geometric stiffness: the geometric stiffness depends on shape, e.g. the stiffness of an I beam is much higher than that of a spring made of the same steel thus having the same rigidity;
• stiffness with hardness: the hardness of a material defines the relative resistance that its surface imposes against the penetration of a harder body;
• stiffness with toughness: toughness is the amount of energy that a material can absorb before fracturing.