(1)Hooke's Law

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  • Created by: Olatunde
  • Created on: 24-03-14 13:31
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Hooke's Law.
Hooke's Law
Robert Hooke was an English physicist who discovered that the force exerted on a
spring is proportional to the extension of the spring.
He created the equation
F = kx
Where
F = Force
x = Change in length (extension)
k = spring constant
Obeying Hooke's Law
Materials only obey Hooke's Law up to a certain force.
Springs can have different stiffness's. A spring which is stiffer
has a higher spring constant, so a larger force is needed to
extend it.
On a graph of force vs. extension, Hooke's law is obeyed in
the linear region (or straight line region) of the graph.
Be careful some materials do not obey Hooke's Law at all
they are not very stiff.
Elastic and plastic
Elastic deformation is when you stretch a spring or material and it returns to the same
length when you take the force off.
Plastic deformation is when you stretch a spring or material and it does not return to the
same length when the force is removed, so the spring is permanently deformed.
On a graph of force vs. extension, when the material stops behaving elastically and begins to
behave plastically, it is the elastic limit the limit of elastic deformation. After this point we get
the plastic region of the graph.
However, the elastic limit is not the proportionality limit. The proportionality limit is simply the
point where force is no longer proportional to extension and so the graph curves (Hooke's law

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But just because the graph is curving, it does not mean it is plastic
deformation.
The experiment
A spring is place on a clamp stand, allowed to hang freely. A ruler is positioned so
that the length of the spring can be accurately measured.
Forces are applied to the spring, and the length or extension is measured.
The results can be recorded.
A graph can be drawn of force vs. extension. The gradient will be the spring
constant of the spring you are using.…read more

Page 3

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The Young's modulus is basically the gradient of a stress strain
graph. Like in a forceextension graph where the gradient is the
spring constant.…read more

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