# Materials

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- Created by: kennedylily
- Created on: 09-04-18 10:28

What is density?

The mass per unit volume of a material or object

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What is the unit of density?

kgm^-3

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What is Hooke's law?

The extension of a stretched object is proportional to the force applied to it (up to the limit of proportionality)

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What is the formula for Hooke's law?

F = kΔL

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What does k represent?

Stiffness/spring constant

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What is an object's stiffness constant?

The force needed to extend the object by 1m

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Give two features of a force-extension graph which show that a material obeys Hooke's law

The graph will be a straight line which goes through the origin

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What does the gradient of a force-extension graph represent?

The stiffness constant, k

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What is the elastic limit?

The force/stress beyond which a material will be permanently stretched

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What is the limit of proportionality?

The point beyond which the force applied is no longer proportional to the extension of an object

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What is the limit of proportionality in relation to a force-extension graph?

The point beyond which the force-extension graph is no longer linear

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When does elastic deformation occur?

When a material returns to its original shape once the forces are removed (ie has no permanent extension)

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When does plastic deformation occur?

When a material is permanently stretched after the forces have been removed

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What is tensile stress?

The force applied to an object divided by its cross-sectional area

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What are the units of tensile stress?

Nm^-2 OR Pa

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What is tensile strain?

The change in length (or extension) divided by the original length of a material

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What are the units of tensile strain?

No units

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What is the breaking stress of a material?

The lowest stress that can be applied to break a material

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What is the ultimate tensile stress of a material?

The maximum stress that a material can withstand

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What is elastic strain energy?

The potential energy stored in a stretched material up to the elastic limit

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What does the area under a force-extension graph represent?

The elastic strain energy

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What is the formula for elastic strain energy?

E = 1/2FΔL

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Describe the energy transformation when a stretched mass-spring system is released

The stored elastic strain energy in the spring is transferred into kinetic energy (as the spring contracts) and gravitational potential energy (as the mass gains height)

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Describe how energy conservation can be applied to transport design

Cars are required to have crumple zones that deform plastically in a crash; this means that some of the car's kinetic energy goes into changing the shape of the car, so less is transferred to the people inside

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What is the Young's modulus of a material?

The tensile stress divided by the tensile strain of a material up to its limit of proportionality

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What does the gradient of a stress-strain graph represent?

The Young's modulus, E

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What does the area underneath a stress-strain graph represent?

The strain energy (or energy stored) per unit volume

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What is the yield point of a material?

The stress at which a large amount of plastic deformation takes place with a constant or reduced load

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What is the shape of a stress-strain graph for a brittle material?

A straight line through the origin until the breaking point (no curve so obeys Hooke's law)

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What makes a material brittle?

It must have a rigid structure

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## Other cards in this set

### Card 2

#### Front

What is the unit of density?

#### Back

kgm^-3

### Card 3

#### Front

What is Hooke's law?

#### Back

### Card 4

#### Front

What is the formula for Hooke's law?

#### Back

### Card 5

#### Front

What does k represent?

#### Back

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