Materials Unit 2 Flashcards
What is density?
The mass per unit volume of a substance
What is hookes law?
The extension of a spring is directily proportional to the force within the limit of proportionality
What is elastic behaviour?
The material goes back to its original shape no matter the extension
What is plastic behaviour?
When the limit of proportionality is exceeded and so the material is permanently extended when the weight is lifted
What is the elastic limit?
When the material stops obeying hookes law and behaves plasticly
What is the limit of proportionality?
When f and x are no longer proportional to each other
How do you calculate the energy stored in a spring?
The area under the graph where it obeys hookes law
How do you work out the k and w for springs in parallel?
Force is w/2
K= k₁+k₂
How do you work out k and w for springs in series?
w is the same for both springs
1/k total = 1/k₁ +1/k₂
What is stress?
The force per unit of cross sectional area.
f/a. Pascals
What is strain?
The ratio between extension and original length.
e/l. No units
What is the yield point?
When the wire weakens temporarily. For a small increase in stress there is a large increase in strain
What is the ultimate tensile stress?
The maximum stress that the material can take before it breaks
What happens when a material is brittle?
It snaps with no noticable yield
What is meant by ductile?
There is a large yield point so it can be drawn into wires.
What does the load extension graph look like for a metal wire?
The wire only unloads if the elastic limit is passed. There is permanent extension
What does the force extension graph look like for a rubber band?
It does not obey hookes law and only unloads if it doesn’t snap. It behaves elasticly
What does the force extension graph look like for polythene?
It is pernamently extended as it suffers plastic deformation.
