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NCERT Physics Grade 11
Deforming force
it is the force which can change the shape and size of an object.
Restoring force
the force developed inside the body against deforming force.
Elasticity
the property of a body to return to its original shape and size after the removal of a deforming force.
Plasticity
when a body doesn’t regain its original shape and size even after the removal of the deforming force.
Stress
internal restoring force set up per unit area of cross-section of deforming body. stress = F/A where F is force applied and A is area of cross-section.
Types of stress
tensile stress: change in length in direction of deforming force
volume stress: uniform force from all sides; change in volume.
tangential stress: force acts tangentially to the surface of the body; change in shape
Strain
ratio of change in dimension produced in the body to original dimension. strain = change in dimension/ original dimension .
Types of strain
longitudinal strain: Δl/l
volume strain: ΔV/V
shear strain: Δx/l
Elastic limit
max stress within which the body regains its original shape after removing deforming force.
Hooke’s Law
for small deformations stress is directly proportional to strain. stress ∝ strain
stress = k strain where k is modulus of elasticity k = stress/strain.
3 modulus’ (Hooke’s law)
Young’s modulus (Y): Fl/AΔl
Bulk modulus (B): FV/AΔV
Sheer modulus (G): Fl/AΔx
ductile vs. brittle material
ductile materials are materials with large plastic range while brittle materials have small plastic range.
Elastomers
materials which can be elastically stretched to large values of strain with little stress.
Elastic after effect
delay in regaining original state of a body on removal of deforming force.
Elastic fatigue
loss in the strength in the material caused due to repeated alternating strains to which the material is subjected.
Elastic energy
work done against the interatomic forces when a wire is put under longitudinal stress is known as elastic energy.
Poisson’s ratio
Ratio of lateral to longitudinal strain.
σ = Δdl/dΔl
