# AQA AS-Level Physics: Materials

What is density?
Mass(kg)/volume(m3)
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What is Hooke's law?
Hooke's Law is the idea that extension is directly proportional to force applied up to the limit of proportionality.
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What is a materials elastic limit?
The maximum amount of load applied to a material before it can no longer return to its original shape.
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What is a materials yield point?
The point where the material begins to stretch without any extra load.
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How do we calculate the spring constant?
Spring constant = Force/extension
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What is the combined spring constant of two springs in series?
1/Ka+1/Kb
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What is the total spring constant if two springs in series are identical?
K/2
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What is the combined spring constant of two springs in parallel?
Ka+Kb
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What is the total spring constant of two springs in parallel are identical?
2K
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How do we calculate energy stored in a spring?
1/2 x (Kinetic Energy ^2)
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How do modern cars use the idea of deformation to reduce the impact on the driver if a car crash happens?
Cars contain crumple zones which deform plastically to reduce the amount of energy transferred to the people in the crash.
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What are compressive and tensile forces?
Compressive forces are forces used to squash a material, tensile forces are forces used to stretch a material.
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What is elastic deformation?
A temporary change in shape of an object once a force is applied. The object returns to its original shape once the load/force is removed.
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What is plastic deformation?
A permanent change in shape of an object because it has passed its elastic limit. So much force has been applied that the object will no longer return to its original shape.
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What is tensile stress? State the formula used to calculate it.
The force applied per unit cross-sectional area (pressure). It causes strain. Tensile stress = Force/Area
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What is tensile strain? State the formula used to calculate it.
A measure of how the stretched material compares to its original length, because it is a ratio, it has no units. Tensile strain = Extension/Original length
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What is the Young Modulus? Give two equations used to calculate it.
The Young Modulus is a measure of how stiff a material is. Young Modulus = Stress (Nm-2 OR Pa)/Strain OR Young Modulus = (Applied force*original length)/(cross sectional area*extension)
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How can elastic strain energy be calculated from a stress/strain graph?
It is the total area underneath the graph.
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The stiffness constant remains the same.
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In a force-extension graph, why do we often find that the unloading line does not pass through the origin?
Because the material has passed its elastic limit and been plastically deformed. The distance between the loading and unloading line is the work done to permanently deform the material
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They fracture as they do not undergo plastic deformation.
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## Other cards in this set

### Card 2

#### Front

What is Hooke's law?

#### Back

Hooke's Law is the idea that extension is directly proportional to force applied up to the limit of proportionality.

### Card 3

#### Front

What is a materials elastic limit?

### Card 4

#### Front

What is a materials yield point?

### Card 5

#### Front

How do we calculate the spring constant?