AS Physics Unit 2: Materials Notes

These are not my notes i just put them in document form, they're from this website ->

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  • Created on: 26-04-14 13:45
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Hooke's Law
Density () is measured in kg m-3. It can be calculated using the equation below;
= density in kg m-3
m = mass in kg
V = volume in m3
Hooke's Law
The extension of a spring or wire is directly proportional to the force applied provided the limit of proportionality is not exceeded.
When a graph of force against extension is plotted for a material which obeys Hooke's law it looks like the graph below.
The gradient of this graph is the spring constant (k) which is measured in Nm-1.

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F = force in newtons (N)
L = change in length in metres (m)
k = spring constant (N m-1)
The limit of proportionality is the is the point beyond which Hooke's law is no longer true when stretching a material.
The elastic limit is the point beyond which the material you are stretching becomes permanently stretched so that the material does not return to its original length
when the force is removed.…read more

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Stress & Strain
The stress applied to a material is the force per unit area applied to the material. The maximum stress a material can stand before it breaks is called the breaking stress
or ultimate tensile stress.
Tensile means the material is under tension. The forces acting on it are trying to stretch the material. Compression is when the forces acting on an object are trying to
squash it.
The equation below is used to calculate the stress.…read more

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L = the limit of proportionality, Hooke's law applies up to this point.
E = elastic limit, beyond this point the material is permanently stretch and it will not go back to its original length. Elastic behaviour is when a material returns to
its original length, plastic behaviour is when the stretched material does not return to its original length.
Y = yield point, beyond this point small increases in force give much big increases in length.…read more

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The energy stored in the stretch wire or spring is the area under the force-extension graph as we can see in the equation below.
E = elastic strain energy in joules (J)
F = force in newtons (N)
L = change in length in metres (m)
Stretching rubber
When rubber is stretched and released energy is lost as heat and this is called hysteresis. The area between the two lines is the energy lost per unit volume.…read more

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Young Modulus
What is a modulus?
A modulus is a numerical value, which represents a physical property of a material .
What is the Young Modulus?
It is the modulus of elasticity. This means it is a number which represents how easy it is to deform (stretch a material).
When a material is stretched stress is directly proportional to strain provided it is not stretched beyond the limit of proportionality.…read more

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L = change in length in metres (m)
Measurement of the Young Modulus
The Young Modulus for a wire can be measured using this equipment. The reference wire and test wire are hung from the ceiling. The reference wire supports a vernier
scale which will measure the extension of the test wire. The force on the test wire can be varied using the slotted masses.
Measurements needed;
1) The original length of the test wire (L) should be measured with a tape measure.…read more


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