Chapter 6 Deformation of Solids Flashcards
Tensile Force
When two forces stretch a body
deformation
Forces don’t just change the motion of a body, but can change the size and shape of them too.
compressive force
When two forces compress a body
Tensile Strenght
Tensile strength is the amount of load or stress a material can handle until it stretches and breaks
different materials beening stretched: steel, rubber and glass
Hooke’s Law
-If a material responds to tensile forces in a way in which the extension produced is proportional to the applied force (load), we say it obeys Hooke’s Law
limit of proportionality
is the point beyond which Hooke’s law is no longer true when stretching a material i.e. the extension is no longer proportional to the applied load
–The point is identified on the graph where the line is no longer straight and starts to curve (flattens out)
A material obeys Hooke’s Law
if its extension is directly proportional to the applied force (load)
Hookes law equation
F = kx
k is the spring constant
of the spring and is a measure of the stiffness of a spring
- A stiffer spring will have a larger value of k
- It is defined as the force per unit extension up to the limit of proportionality (after which the material will not obey Hooke’s law)
- The SI unit for the spring constant is N m-1
Spring constants for springs combined in series and parallel
Stress (or tensile stress)
Tensile stress is the applied force per unit cross sectional area of a material
-The ultimate tensile stress is the maximum force per original cross-sectional area a wire is able to support until it breaks σ = F/A.
σ-stress(Pa) F=Force(N) A=Cross-sectional area (m^2)
Strain
- Strain is the extension per unit length
- This is a deformation of a solid due to stress in the form of elongation or contraction
- Note that strain is a dimensionless unit because it’s the ratio of lengths ε = x/L ε-strain x-extension(m) L-length (m)
how to find the cross-sectional area A
Young’s Modulus
- The Young modulus is the measure of the ability of a material to withstand changes in length with an added load ie. how stiff a material is
- This gives information about the elasticity of a material
- The Young Modulus is defined as the ratio of stress and strain Young’s modulus = stress/strain = (FL0)/A(Ln − L0). -its unit is the same as stress: Pa (since strain is unitless)