# Materials

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State Hooke's law (applies for compressive and tensile forces - includes springs)
Extension is proportional to force. F = kx (k is the force constant or spring constant and has units Nm^-1)
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What is it called when the force becomes great enough and the Force/extension graph starts to curve?
the limit of proportionality
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What happens if you exceed the elastic limit?
The material is perminantly stretched. Elastic before and plastic after.
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You can combine k in parallel or in series. Show how you combine the force constants depending on how the springs are arranged
Series: 1/k = 1/k1 + 1/k2. Parallel: k = k1 + k2
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Define elastic deformation
the material returns to its origional shape once the forces are removed (under tension the atoms are pulled apart and move slightly relative to their equilibrium positions but return once the load is removed)
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Define plastic deformation
the material is permanently stretched (some atoms move position relative to one another, when the load is removed the atoms dont return to their original positions)
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What is tensile stress? and what is tensile strain? (compressive is the same just negative)
Stress = Force(F)/cross-sectional area(A) - in Nm^-2 or Pa. Strain = change in length(x)/original length(l)
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The effect of stress is to start to pull the atoms apart from each other. What is Ultimate tensile strength/
The maximum stress a material can take before breaking (breaking stress here) . Atoms separate completely here.
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When a material is stretched or compressed, work is done in deforming the mterial. What is Elastic Potential energy?
the energy stored in a stretched material. Area under graph of Force/extension
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What is work done on the wire in stretching it
The same as the energy stored. Work done = 1/2Fx (average force because force isnt constant)
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Because Hooke's law is being obeyed and F = kx...
E = 1/2kx^2. up to elastic limit as work is done separating atoms - wont be stored as elastic potential energy - isnt released when force removed)
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Young modulus =
tensile stress / tensile strain. (Nm^-2 or Pa)
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Area under Stress/Strain graph =
elastic potential energy
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Energy per unit volume =
1/2 x stress x strain
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What is the yield point? (ductile materials)
the stress at which a large amount of plastic deformation takes place with a constant or reduced load. (the material suddenly starts to stretch without any extra load)
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What is different about the graph of a brittle material?
the graph starts the same with a straight line through the origin. But when the stress reaches a certain point, the material snaps (tiny cracks getting bigger until material breaks) - brittle fracture
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## Other cards in this set

### Card 2

#### Front

What is it called when the force becomes great enough and the Force/extension graph starts to curve?

#### Back

the limit of proportionality

### Card 3

#### Front

What happens if you exceed the elastic limit?

### Card 4

#### Front

You can combine k in parallel or in series. Show how you combine the force constants depending on how the springs are arranged

### Card 5

#### Front

Define elastic deformation