Elasticity, Stress, and Strain
Elasticity is a measure of how much an object deforms (strain) when a given stress (force) is applied.
Learning Objective

Identify properties of elastic objects
Key Points
 Elasticity is a measure of the deformation of an object when a force is applied. Objects that are very elastic like rubber have high elasticity and stretch easily.
 Stress is force over area.
 Strain is change in length over original length.
Term

deformation
A transformation; change of shape.
Full Text
We now move from consideration of forces that affect the motion of an object (such as friction and drag) to those that affect an object's shape. If a bulldozer pushes a car into a wall, the car will not move once it hits the wall, but it will noticeably change shape. A change in shape due to the application of a force is a deformation. Even very small forces are known to cause some deformation. For small deformations, two important characteristics are observed. First, the object returns to its original shape when the force is removed—that is, the deformation is elastic for small deformations. Second, the size of the deformation is proportional to the force—that is, for small deformations, Hooke's law is obeyed. In equation form, Hooke's law is given by
Elasticity is a measure of how difficult it is to stretch an object. In other words it is a measure of how small
Stress is a measure of the force put on the object over the area.
Strain is the change in length divided by the original length of the object.
Experiments have shown that the change in length (ΔL) depends on only a few variables. As already noted, ΔL is proportional to the force F and depends on the substance from which the object is made. Additionally, the change in length is proportional to the original length L0 and inversely proportional to the crosssectional area of the wire or rod. For example, a long guitar string will stretch more than a short one, and a thick string will stretch less than a thin one .
Tension/Compression
Tension: The rod is stretched a length ΔL when a force is applied parallel to its length. (b) Compression: The same rod is compressed by forces with the same magnitude in the opposite direction. For very small deformations and uniform materials, ΔL is approximately the same for the same magnitude of tension or compression. For larger deformations, the crosssectional area changes as the rod is compressed or stretched.
Key Term Reference
 Hooke's law
 Appears in these related concepts: Sinusoidal Nature of Simple Harmonic Motion, Springs, and Simple Harmonic Motion
 Law
 Appears in these related concepts: Damped Harmonic Motion, Photon Interactions and Pair Production, and Models, Theories, and Laws
 Length
 Appears in these related concepts: Atomic Structure, Length, and Introduction to The Sampling Theorem
 application
 Appears in these related concepts: Introduction to Elementary operations and Gaussian Elimination, Physics and Other Fields, and XRay Imaging and CT Scans
 elastic
 Appears in these related concepts: Defining Price Elasticity of Demand, Applications of Elasticities, and Tax Incidence, Efficiency, and Fairness
 elasticity
 Appears in these related concepts: Hooke's Law, Speed of Sound, and Impact of Price on Consumer Choices
 equation
 Appears in these related concepts: Equations and Inequalities, Graphs of Equations as Graphs of Solutions, and What is an Equation?
 force
 Appears in these related concepts: Force of Muscle Contraction, Force, and First Condition
 friction
 Appears in these related concepts: Friction: Static, ProblemSolving With Friction and Inclines, and Inelastic Collisions in Multiple Dimensions
 motion
 Appears in these related concepts: Motion Diagrams, TwoComponent Forces, and Moving Source
 strain
 Appears in these related concepts: Fracture, Stress and Strain, and Sprain and Strain
 stress
 Appears in these related concepts: Stress and Immunity, Thermal Stresses, and Causes of Workplace Stress
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