In earlier mechanics we were concerned with the effects on the state of motion of a body caused by the forces upon it. Now we are concerned with the effects of force on the shape of the body itself. A solid body under load experiences a deformation. A deformation is considered elastic if, when the load is removed, the object returns to its original shape.

Elasticity appears fairly regularly on the MCAT, and the basics of this discipline, which is often neglected in lecture course, are pretty easy to master. On the exam, you may be expected to distinguish the three common types of deformation, elongation, shearing and compression, and their corresponding moduli, for example, or you may be asked to distinguish an elastic from a non-elastic deformation.

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Conceptual Vocabulary for Elasticity

Elasticity

Elasticity is a branch of physics which studies the properties of materials which deforms under stress, but then return to their original shape when the stress is removed.

Elasticity is a branch of physics which studies the properties of materials which deforms under stress, but then return to their original shape when the stress is removed.

Stress

Stress is a measure of force per unit area within a body. It is a body's internal distribution of force per area that reacts to external applied loads.

Stress is a measure of force per unit area within a body. It is a body's internal distribution of force per area that reacts to external applied loads.

Strain

Strain is the geometrical expression of deformation caused by the action of stress on a physical body.

Strain is the geometrical expression of deformation caused by the action of stress on a physical body.

Shear strain

Shear strain is a strain that acts parallel to the face of a material that it is acting on.

Shear strain is a strain that acts parallel to the face of a material that it is acting on.

Shear modulus

Shear modulus is defined as the ratio of shear stress to the shear strain.

Shear modulus is defined as the ratio of shear stress to the shear strain.

Shear stress

Shear stress is a stress state where the stress is parallel or tangential to a face of the material.

Shear stress is a stress state where the stress is parallel or tangential to a face of the material.

Hooke's law

Hooke's law of elasticity is an approximation that states that the amount by which a material body is deformed is linearly related to the force causing the deformation.

Hooke's law of elasticity is an approximation that states that the amount by which a material body is deformed is linearly related to the force causing the deformation.

Normal stress

Normal stress is stress that acts perpendicular to the face of the material, a compression or a tension.

Normal stress is stress that acts perpendicular to the face of the material, a compression or a tension.

Elastic modulus

The slope of its stress-strain curve in the elastic deformation region, the elastic modulus describes an object's tendency to be deformed elastically under load.

The slope of its stress-strain curve in the elastic deformation region, the elastic modulus describes an object's tendency to be deformed elastically under load.

Tensile stress

Tensile stress, or tension, is the stress state leading to expansion.

Tensile stress, or tension, is the stress state leading to expansion.

Bulk modulus

The bulk modulus of a substance essentially measures the substance's resistance to uniform compression.

The bulk modulus of a substance essentially measures the substance's resistance to uniform compression.

Deformation

Often described in terms of strain, deformation is a change in shape due to an applied force.

Often described in terms of strain, deformation is a change in shape due to an applied force.

Normal strain

Normal strains produce dilations without a shape-change as such.

Normal strains produce dilations without a shape-change as such.

Young's modulus

Young's modulus is a measure of the stiffness of a given material, also known as the tensile modulus.

Young's modulus is a measure of the stiffness of a given material, also known as the tensile modulus.

Stiffness

Stiffness is the resistance of an elastic body to deflection or deformation by an applied force.

Stiffness is the resistance of an elastic body to deflection or deformation by an applied force.

Yield

The yield point of a material is the stress at which a material begins to plastically deform.

The yield point of a material is the stress at which a material begins to plastically deform.

Rigid body

A rigid body is an idealization of a solid body of finite size in which deformation is neglected.

A rigid body is an idealization of a solid body of finite size in which deformation is neglected.

Plasticity

Plasticity is a property of a material to undergo a non-reversible change of shape in response to an applied force.

Plasticity is a property of a material to undergo a non-reversible change of shape in response to an applied force.

Fracture toughness

Fracture toughness is a property which describes the ability of a material containing a crack to resist fracture.

Fracture toughness is a property which describes the ability of a material containing a crack to resist fracture.

Stress-strain curve

A stress-strain curve is a graph derived from measuring load versus extension for a sample of a material.

A stress-strain curve is a graph derived from measuring load versus extension for a sample of a material.

Hysteresis

Hysteresis is a property of systems that do not instantly react to the forces applied to them, but react slowly, or do not return completely to their original state.

Hysteresis is a property of systems that do not instantly react to the forces applied to them, but react slowly, or do not return completely to their original state.

Ductility

Ductility is the mechanical property of being capable of sustaining large plastic deformations due to tensile stress without fracture.

Ductility is the mechanical property of being capable of sustaining large plastic deformations due to tensile stress without fracture.

Toughness

Toughness is the resistance to fracture of a material when stressed, defined as the amount of energy that a material can absorb before rupturing.

Toughness is the resistance to fracture of a material when stressed, defined as the amount of energy that a material can absorb before rupturing.

Viscoelasticity

Viscoelasticity, also known as anelasticity, describes materials that exhibit both viscous and elastic characteristics when undergoing plastic deformation.

Viscoelasticity, also known as anelasticity, describes materials that exhibit both viscous and elastic characteristics when undergoing plastic deformation.

Rheology

Rheology is the study of the deformation and flow of matter under the influence of an applied stress.

Rheology is the study of the deformation and flow of matter under the influence of an applied stress.