Deformation of solids
Solids change their shape when we pull them or push them, and at Advanced Subsidiary level we learn to describe that change with real precision. We begin with tensile and compressive forces, the words load, extension and compression, and Hooke's law F = kx with its spring constant k. We meet the limit of proportionality, the elastic limit and the yield point, combine springs in series and in parallel, and then step up to the quantities that describe a material rather than a single wire: tensile stress σ = F/A, tensile strain ε = x/L, and the Young modulus E = stress ÷ strain. We read force–extension and stress–strain graphs, tell elastic from plastic behaviour, recognise ductile, brittle and polymeric curves, and finally find the elastic strain energy stored in a stretched material from the area under the graph, Ep = ½Fx = ½kx².
By the end you should be able to (NSSCAS Physics (AS) 1.7):
- Outline that deformation is caused by a force and that, in one dimension, it can be tensile or compressive; use the terms load, extension and compression
- Explain and use the terms limit of proportionality, elastic limit, yield point and the spring constant (force per unit extension)
- Recall and use Hooke's law, F = kx, and obtain the spring constant from the gradient of a force–extension graph
- Combine springs in series and in parallel and describe the effect on the effective spring constant
- Define and use tensile stress σ = F/A and tensile strain ε = x/L
- Define and use the Young modulus E = stress ÷ strain, and describe an experiment to determine it for a metal wire
- Distinguish between elastic (reversible) and plastic (permanent) deformation, and interpret ductile, brittle and polymeric stress–strain graphs
- Relate the area under a force–extension graph to the work done, and recall and use Ep = ½Fx = ½kx² for the elastic strain energy
Miss Elizabeth and Mike talk through the whole topic — with the figure and working drawn live.