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IGCSE Combined Science
NOT THIS ONE! Hooke’s Law IGCSE Combined Science
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What did Hooke discover ?
the more force that was put on materials the more they extended With some materials they also extended in a regular way -eg. if the force was doubled so did the extension this was true as long as their elastic limit was not exceeded
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What is the elastic limit?
Is when the material no longer shows elastic behavior -ie does not return to original size when stretching force is removed The material is permanently deformed -i.e. is larger or longer than originally
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Hookes Law states: Force is proportional to extension F α x
Or if k is the proportionality constant F = kx
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What does k mean in F=kx? k is called the spring constant and is a measure of the stiffness of the spring or material It has units of Nm-1 (newtons per metre) The higher the k the stiffer the spring Materials with a high k need a large force for a given extension
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The spring constant k is measured in Nm-1 because it is the force per unit extension.
The value of k does not change unless you change the shape of the spring or the material that the spring is made of.
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Example A spring is 0.38m long. When it is pulled by a force of 2.0 N, it stretches to 0.42 m. What is the spring constant? (Assume the spring behaves elastically.) Extension, x = Stretched length – Original length = 0.42m – 0.38m = 0.04 m 2.0N = k x 0.04m So, k = 2.0 N 0.04 m = 50 N m-1
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