Physics- Unit 2- Materials

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  • Created by: FireDwarf
  • Created on: 29-01-14 21:01
What is density?
Mass/ Volume
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kg m-3
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Density of water?
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Relative density equation?
Density/ Density of water (1000)
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How to measure density for a regular solid?
Measure its mass using a balance and work out volume using appropiate formula (eg: volume of a cylinder).
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A liquid?
Measure mass of cylinder and then mass of water + cylinder, take cylinder from water. Measure volume using a measuring cylinder.
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Irregular solid?
Measure mass of object. Immerse the object in water and observe the increase in water level, this is your volume.
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What is Hookes law?
The extension of a spring is directly proportional to the force applied.
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Proportional positive correlation up to elastic limit, where afterwards we it curving downwards.
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f= K change in L. (K spring constant).
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Parallell springs, what is the force needed to stretch?
Strench spring 1 = kp change in L. Spring 2, kp change in L.
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Weight? (Force)
W = k change in L (added k's & added change in lenghs).
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Series springs, what is the extension of the two spirngs?
Total = w/kp + w/kq. (w/total k)
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How to work out total k?
1/kq + 1/kp
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What does the area under Hookes law graph mean? Gradient?
The elastic potential area stored by the spring & gradient is k.
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What is elasticity?
The ability for a material to retain is shape and size after it has been deformed and the force has been released.
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What is tensile?
A force which streches an object?
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Compresses an object.
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What is stress?
(o with a line) T/A (T = Tension/Force) / Cross sectional area (Pascals)
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(werid looking E) Change in lengh/original lengh (NO UNIT, RATIO)
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Young Modulus?
Stress/Strain pascals (Proper E)
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How to plot a stress strain graph?
Stress, y axis, strain x axis.
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What does p,e,y,y2,uts & b mean?
P- Point of proportionality. e- Elastic limit y- Between y and y2- yield point (where sire becomes weakened tempoary)- uts- Ultimate tensile stress - breaking stress
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So what does P mean?
Point where proportionality of stress and strain is lost.
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Elastic limit?
After this, the wire is permenantly streched and suffers plastic deformation.
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Yield? UTS? Breaking stress?
Between Y1- Y2, the wire becomes weakened. Beyond Y2, small increase in stress causes large increase strain. Beyond max, wire loses strenth. B- (Breaks.)
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How to compare stiffness of materials?
Youngs Modulus
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High stress for a low strain
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Demostrates elastic behaviour
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What is the loading and unloading curve for a metal wire providing its elastic limit has not been exceeded?
A straight line (plastic behaviour)
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What if its elastic limit is exceeded?
the unloading line becomes parrell to the loading line, it has a permement extension.
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What about a rubber band?
change in lengh unloading is greater then loading. Returns to same unstreched lengh, but the unloading is below the loading curve. It has a low limit of proportionality.
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Polythene *****?
extension during unloading is greater then during loading. Does not return to original lengh when unloaded compeletly. It therefore suffers plastic deformation.
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Card 4


Relative density equation?


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Card 5


How to measure density for a regular solid?


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