Hooke's Law (OCR A Level Physics)

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Katie M

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Hooke's Law

  • When a force F is added to the bottom of a vertical metal wire of length L, the wire stretches
  • A material obeys Hooke’s Law if:

The extension of the material is directly proportional to the applied force (load) up to the limit of proportionality

  • This linear relationship is represented by the Hooke’s law equation:

Hooke's law equation, downloadable AS & A Level Physics revision notes

 

  • The spring constant, which is sometimes called the force constant k, is a property of the material being stretched and measures the stiffness of a material
    • The larger the spring constant, the stiffer the material

  • Hooke's Law applies to both extensions and compressions:
    • The extension of an object is determined by how much it has increased in length
    • The compression of an object is determined by how much it has decreased in length

Worked example

A spring was stretched with increasing load.

The graph of the results is shown below.

WE - hookes law question image, downloadable AS & A Level Physics revision notes

What is the spring constant?

Worked example hookes law - 2, downloadable AS & A Level Physics revision notesWorked example hookes law - 3, downloadable AS & A Level Physics revision notesWorked example hookes law - 4, downloadable AS & A Level Physics revision notes

Examiner Tip

Always double-check the axes before finding the force constant as the gradient of a force-extension graph.Exam questions often swap the force (or load) onto the x-axis and extension (or length) on the y-axis. In this case, the gradient is not the force constant, it is 1 ÷ gradient instead.

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Katie M

Author: Katie M

Expertise: Physics

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.