Elasticity is the capacity of a deformed object to come back to its original size and shape when the forces creating the deformation are released. An object with this capacity is considered to behave elastically. To a lesser or greater extent, most solid things show elastic nature, but there is a limit to the force’s magnitude and the resulting deformation within which elastic recuperation is viable for any given object. This limit, known as the elastic limit, is the maximum force per unit area or stress within a solid object that can adjust before permanent deformation.
Stress forces beyond the elastic threshold cause material to flow or yield. In these cases, the elastic limit represents the end of elastic nature and the start of the plastic behaviour. In the case of brittle objects, stresses over the elastic limit produce fracture with negligible plastic deformation. The fundamental reasons for elastic behaviour are much different for different substances. For metals, the atomic lattice varies in shape and size when external forces are applied. When the external forces are withdrawn, the lattice returns to the default lower energy state. For polymers (e.g., rubber), elasticity is generated by the stretching of polymer chains when forces are exerted.
Hooke’s law shows that the force needed to deform elastic materials must be directly proportional to the deformation length, in spite of how big that length becomes. This is called perfect elasticity, in which a given material will return to its default shape regardless of how extremely it is deformed. This is a theoretical model only; most objects which have elasticity in practice stay purely elastic only up to minimal deformations, after which permanent or plastic deformation happens.
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Important Elasticity Questions with Answers
1) What is elasticity?
Elasticity is the capacity of a deformed object to come back to its original size and shape when the forces creating the deformation are released. An object with this capacity is considered to behave elastically. To a lesser or greater extent, most solid things show elastic nature, but there is a limit to the force’s magnitude and the resulting deformation within which elastic recuperation is viable for any given object. This limit is known as the elastic limit.
2) What happens to a rigid body when external forces are applied to it?
When external forces are exerted on a rigid body, there will be a variation in its length, shape or volume.
3) What is the property of a body that allows it to come back to its original shape or size when external forces are removed?
The property of a body that allows it to come back to its original shape or size when external forces are removed is called elasticity.
4) What are elastic stress and strain?
Elastic stress and strain are the internal force and deformation, respectively, experienced by an elastic body under external forces.
5) What happens to internal and external forces when an elastic body is deformed?
When an elastic body is deformed, internal restoring forces are generated that oppose the external forces.
6) How is stress defined?
Stress is defined as the force per unit area of a material.
7) What are the three types of stress?
The three types of stress are longitudinal stress, volume stress (bulk stress) and tangential stress (shear stress).
8) What is longitudinal stress?
Longitudinal stress is stress that is normal to the surface area of the body and causes a change in the length of the body.
9) What are the two types of longitudinal stress?
The two types of longitudinal stress are tensile stress and compressive stress.
10) What is tensile stress?
Tensile stress is longitudinal stress produced due to an increase in the length of the object.
11) What is compressive stress?
Compressive stress is longitudinal stress produced due to the decrease in the length of the object.
12) What is volume stress?
Volume stress is the stress that occurs when equal normal forces are applied to the body, causing a change in the volume of the body.
13) What happens to the volume of a body when it experiences volume stress?
The volume of a material changes significantly when it is under volume stress. The change in the body’s volume under bulk stress per unit of the original volume can be stated as volume strain or bulk strain.
14) What is tangential stress?
Tangential stress is stress that is tangential (or parallel) to the surface of the body.
15) What happens to the shape of a body when it experiences tangential stress?
When a body experiences tangential stress, its shape changes or it gets twisted.
16) What is meant by strain?
Strain is the fractional change in the dimension of a body produced by the external stress acting on it.
17) How is strain calculated?
Strain is calculated by taking the ratio of the change of any dimension to its original dimension.
18) Does strain have a unit or dimension?
Strain does not have a unit or dimension.
19) What is the fractional change in the dimension of a body produced by external stress called?
The fractional change in the dimension of a body produced by external stress is called strain.
20) What is the ratio of change of any dimension to its original dimension called?
The ratio of change of any dimension to its original dimension is called strain.
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Practice Questions
1) What are the factors controlling elasticity?
2) What is the difference between stress and strain?
3) What is the difference between tensile stress and compressive stress?
4) Define Poisson’s ratio.
5) A metal pipe is positioned between two fixed pillars and heated. What kind of stress is generated over the pipe?
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