materials

• density is defined as the mass per unit volume
• a final answer must be given to the same number of significant figures as the data used that has the lowest number of significant figures
• Hooke's Law states that the force needed to stretch a spring is directly proportional to the extension of the spring from its natural length

  $F=$$kΔL$
• when a spring is stretched energy is transferred to the elastic potential energy store of the spring

  $Ep=$$1/2 FΔL$
• the elastic limit is the point beyond which the material will become permanently stretched
• the limit of proportionality is the point beyond which the material will no longer obey Hooke's Law
• the area under a force-extension graph tells you the energy stored
• tensile stress is defined as the force (or tension) per unit area

  $σ=$$F/A$
• Tensile strain is defined as the ratio of extension to the original length.

  $ε=$$ΔL/L$
• the Young's modulus of a material is the stress applied to it per unit strain

  young's modulus = stress/strain

  $E=$$σ/ε$or $E=$$FL/AΔL$
• gradient of a stress-strain graph is the young's modulus
• the area under a stress-strain graph is the elastic strain energy per unit volume
• brittle = breaks without any noticeable yield
• ductile = can be drawn into a wire "exhibits plastic behaviour"
• the area between the loading and unloading curves represents the increase in internal energy of the molecules
• the area between the loading and unloading curves represents the increase in internal energy of the molecules and the work done to deform the object
• the work done to deform an object is referred to as strain energy