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Consider the following pictures. AL- HOCEIMA EARTHQUAKE 24 /02 /2004. Consider the following pictures. Consider the following pictures. Hooke’s Law. Robert Hooke 1635-1703.

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slide1

Consider the following pictures

AL-HOCEIMA EARTHQUAKE

24 /02 /2004

robert hooke 1635 1703
Robert Hooke 1635-1703
  • Researched and wrote papers on Geometry, Snowflakes, Heat, Astronomy, Fossils, Air Pumps, Light, Watches, Telescopes and Silkworms…..among other things.
  • Hooke’s Law was one of the few things he was popularly credited with creating.
  • A rather crabby individual but credited with also inventing the universal joints, the balance wheel and the iris diaphragm
what did hooke discover about forces
What did Hooke discover about forces ?
  • the more force that was put on materials the more they extended
  • With some materials they also extended in a regular way e.g.- if the force was doubled so did the extension
  • this was true as long as their elastic limit was not exceeded
lets try an activity
Lets try an activity
  • Read the instructions on lab sheet provided.
  • Arrange apparatus and perform experiments.
  • Analyse and present data
what is the elastic limit
What is the elastic limit?
  • The material no longer shows elastic behaviour (i.e. does not return to original size when stretching force is removed)
  • The material is permanently deformed i.e. is larger or longer than originally
  • The material is weaker as the above effects are caused by fracture of some atomic bonds
hence in general the force is proportional to extension so hooke s law could be put as

Hence in general, the Forceis proportional toextension.SoHooke’s Law could be put as

Where F is the applied force in Newtons

x is the extension in metres

Or if k is the proportionality constant F=kx

what does k mean in f kx
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 to for a given extension
  • adding springs in series or parallel changes k
series and parallel springs

k decreases by 2

Combined springs slacken compared with single spring extension doubles

Series and parallel springs

Parallel

Series

k increases by 2

Combined springs stiffen compared with single spring

extension halves

so how does this help me
So how does this help me?
  • Understanding Hooke’s law is critical to the construction of any structure eg bridges or buildings.
  • During earthquakes deformations of buildings occur.
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Summary

Hooke’s law explains how a material’s extension/deformation depends on the applied force.Deformation of materials though in practice is looked at in terms of stress ( the force per square metre) and strain (the extension per unit length) are more commonly used instead of simply force and extension