1.3.4 BEHAVIOUR OF SPRINGS & MATERIALS

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What causes deformation?
a force in one dimension that can be tensile or compressive
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What is a compressive force?
force than is applied to shorten or compares an object
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What is a tensile force?
force that is applied to stretch or lengthen an object
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On a Force vs. extension graph, what is the gradient?
spring constant, k
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On a Force vs. extension graph, what does the area under the line represent?
the work done
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What is an elastic limit?
value of the stretching force beyond which a sample becomes permanently deformed
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What is Hooke's Law?
extension, x, is directly proportional to the applied force, F
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What is stress? - What are it's units?
force acting per cross-sectional area - units are Pascals
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What is strain? - What are its units?
the extension produced per unit length - no units
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What is Young's modulus?
stress/strain - the stiffness of a material being stressed
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When will a material obey Hooke's Law?
if it;s extension is directly proportional to the applies force - true so long as the materials elastic limit is not exceeded
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How can you also calculate Young's Modulus? - What is it's unit?
the gradient, E, of a stress vs. strain graph - unit pascals
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What is elastic potential strain energy?
energy stores when an object is stretched/ compressed
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What happens to EPSE when an object is elastically strained?
energy can be reverted back
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What happens to EPSE when an object is plastically strained?
some energy goes into moving atoms etc. this energy cannot be recovered
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How can you calculate the EPSE stored in a wire?
calculate average work done, kx^2/2 or area under f vs. x graph
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What happens when an object is deformed?
work is done and the energy is transferred into strain energy in the material
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Describe an experiment to estimate Young's modulus of a material
wire of known length/ micrometer to calc cross-sectional area // 1. fix wire at one end and place marker on wire 2. add smallest weight, measure distance between fixed point and marker 3. increase weight at reg. intervals measuring extension
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How would you use the results from your experiment to calculate Young's modulus?
calc force from load // use results to plot graph f vs. x // gradient of F vs x multiplied by L/A
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Describe the equation to calculate Young's modulus
stress/strain = F/A / x/L = FL/xA = Work done/ volume
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What is elastic deformation?
material returns to it's original shape when forces removed
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What is plastic deformation?
material does not return to it's original shape when forces removed
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What is ultimate tensile strength?
stress value at which material breaks (breaking stress) (MAX STRESS)
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Describe the extension of a brittle material
material is strong as there is little x for high stress// but further increase in applied stress causes fracture// behave elastically until fracture // will shatter if sudden application
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Describe the extension of a ductile material
behaves elastically up to limit// permanent deformation once enters plastic region
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Describe the extension of a polymeric material
behaviour depends on temp/molecular structure // will undergo deformation of either elastic or plastic type depending on material
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Other cards in this set

Card 2

Front

What is a compressive force?

Back

force than is applied to shorten or compares an object

Card 3

Front

What is a tensile force?

Back

Preview of the front of card 3

Card 4

Front

On a Force vs. extension graph, what is the gradient?

Back

Preview of the front of card 4

Card 5

Front

On a Force vs. extension graph, what does the area under the line represent?

Back

Preview of the front of card 5
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