Materials

What is Hooke’s Law?

for a material within its elastic limit, force is directly proportional to the extension

What is Hooke’s Law equation?

F=kx

What is elastic deformation?

where the material will return to its original shape once force is removed

What is plastic deformation?

when force is removed the material will have permanent deformation, not returning to original shape

What is the force extension graph of a metal wire?

obeys hooke’s law until elastic limit. loading curve the same as the unloading curve, showing permanent extension

What is the force extension graph of a spring?

obeys hooke’s law until elastic limit, then plastic deformation

What is the force extension graph for rubber?

does not obey hooke’s law, area is a hysteresis loop. energy required to stretch the material is transferred to thermal when force removed

What is the force extension graph of polyethene?

does not obey hooke’s law, has plastic deformation when any force is applied

Describe how to investigate force-extension characteristics

material is suspended using a clamp stand with a clamp and boss, adjacent to a metre ruler. a marker is applied to mark original length. masses are then attached to the end of the material, and extension for each is recorded. graph of force against extension

How to reduce error in force-extension experiment

use a set square, eye level. use the gradient of the straight section - during elastic limit

What is the force constant in series?

1/k + 1/k2 + 1/k3 = 1/ktotal

What is the force constant in parallel?

k1 + k2 + k2 = ktotal

What is the area under a force extension graph?

elastic potential energy

What is elastic potential energy?

energy transferred to the material when work is done while the material is deformed elastically

What is the equations for elastic potential energy?

E = 1/2Fx

E = 1/2ke²

What is stress and its formula?

force applied to a material per unit cross-sectional area

stress = F/A (Pa)

What is strain and its formula?

extension/compression of a material per unit of its original length, no units

strain = x/L

What is young’s modulus and its formula?

ratio of stress to strain - gradient of stress strain graph

E = stress/strain

Describe how to find young’s modulus of a metal wire

use a micrometer to measure diameter of the wire to find area. wire is clamped at one end and suspended using a pulley, a ruler placed parallel to measure extension. different forces applied using masses, mass and extension recorded. calculate stress and strain and plot, find gradient

What is ultimate tensile strength?

maximum stress that can be applied before a material breaks

Stress strain graph for glass

straight line - no plastic deformation

stress strain graph for elastic material

no plastic deformation, unloading curve different to loading curve

Stress strain of a ductile material

elastic deformation until elastic limit, then plastic deformation before UTS and breakpoint