Exam Frequency Analysis
Past paper frequency (2018 to 2024)
This topic accounts for approximately 14% of your exam marks.
stable
High
Stable14%
F = ma, resultant forces and Hooke's Law calculations are high-frequency multi-mark questions.
The law
- Hooke's law states that, up to the limit of proportionality, the extension of an elastic object (such as a spring) is directly proportional to the force stretching it
- Directly proportional means:
- doubling the stretching force doubles the extension
- halving the stretching force halves the extension
- a plot of force against extension is a straight line through the origin within the proportional region
Limit of proportionality
- Every elastic material has a limit of proportionality, a stretching force beyond which extension no longer keeps step with the force
- Past this limit, the force-extension graph bends away from its straight section: each extra newton produces a larger extra extension than before
- The exact value of the limit depends on the material and on its dimensions
Elastic and inelastic deformation
- Deformation is any change in an object's original shape produced by a force
- Two outcomes are possible when the force is removed:
- Elastic deformation, where the object returns to its original shape and size. Examples: a steel spring, a rubber band, most fabrics, a tennis ball after a bounce
- Inelastic deformation (also called plastic deformation), where the object stays permanently changed even after the force is removed. Examples: a clay tile that has been moulded, a paperclip that has been bent past straightening, a sheet of glass that has been cracked
- Hooke's law is a statement about the elastic region of a material; once a material has been pushed into inelastic deformation, it does not spring back to the origin of the force-extension graph