ELASTICITY

Stress and Strain

Tensile Stress- the ratio of the magnitude of the applied force F to the cross-sectional area A:

Mathematically,

Stress= Force/Area=F/A

Another internal force is called tensile strain.

Tensile strain- defined as the ratio of the change in length ∆L to the initial length L₀ before the force was applied. This strain refers to an increase in length.

In equation form,

Strain= change in length /initial length

=∆L/L₀

The strain is the fractional change in length. The bar would deform also if it were under compressive force, but this time it would be compressed rather than stretched; The bar is under compressive strength.

Compressive strain- opposite of tensile strength, causes the bar to be compressed.

If the stress is not too great, the strain is observed to be proportional to the stress. The ratio of a stress to the corresponding strain is called an elastic modulus, Young’s modulus.

Young’s Modulus of Elasticity- ratio of a stress to the corresponding strain (tensile or compressive), on an object.

The equation of Y is given by

Y= stress/strain= (F/A)/(∆L/L₀)

Young’s Modulus values of some materials are indicated in the book; e-Physics

Elastic Limit

Obviously, if the objects stress is large, it will definitely break. It has reached its elastic limit.

Elastic Limit- refers to the maximum stress that can be applied to an object without its breaking up, or being permanently deformed

But not everything who reach its elastic limit breaks. The Bone remains elastic even if its breaking point is already reached, which means, its size or shape doesn’t change by applying force.

Heat does something with the elastic limit, Which why metals are often heated before being formed into shaped by bending or hammering.