what is plastic deformation?
when the force applied to an object is removed and the material doesn’t return back to its original shape/remails partially deformed
what is elastic deformation?
when the force applied to an object is removed and the material returns back to its original shape
what is Hooke’s law (equation)?
force = spring constant x extension
what is the equation for elastic potential energy?
energy = 1/2 x spring constant x extension^2
how do we find the spring constant of springs in series?
1/k = 1/k1 + 1/k2…
how do we find the spring constant of springs in parallel?
k = k1 + k2…
what does the area under a force-extension graph represent?
the elastic potential energy
what does the gradient of a force-extension graph represent?
spring constant
what is the equation of strain?
strain = extension (m2) / original length (m2)
what is the equation for Youngs Modulus?
energy (Pa) = stress (Pa) / strain
what is a brittle material?
a strong material that will break without having a region of plastic deformation
what is a ductile material?
material that can be stretched into wires because it has a large plastic region
what is Youngs Modulus?
measure of stiffness of a material without taking into account the dimensions
how can Youngs Modulus be found with a stress-strain graph?
gradient
what happens when a material has a high Youngs Modulus?
more stiff
what happens when a material has a low Youngs Modulus?
flexible
what are the similarities between k and E?
both measurements of stiffness (applied when obeying Hooke’s Law)
what are the differences between k and E?
E never changes as it doesn’t depend on dimensions
what are the properties of rubber?
- doesn’t obey Hookes Law but returns to original shape
- Hysteresis loop represents energy transferred from stretching to thermal
- work done unloading is equal to the thermal energy released
what are the properties of polythene?
- doesnt obey Hookes Law
- experiences plastic deformation when force applied
- easy to stretch into new shapes
what are the properties of a metal wire?
- obeys Hookes Law
- shows elastic deformation until elastic limit
- unloading equals loading in this region
- experiences plastic deformation after elastic limit
- unloading curve has permanent extension
how do we work out thermal energy from a graph?
count number of boxes
what is ultimate tensile strength?
maximum stress a material can withstand
