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Hooke's Law states: The extension of a wire is directly proportional to the force applied.
Force (F) = constant (k) x extension (e)
Hooke's law also applies to springs.
- The expansion or compression of a spring is proportional to the force applied.
Hooke's law stops working when the load is great enough.
If you increase the load past the elastic limit, the material will become permanently stretched.
- Metals generally obey Hooke's law up to the limit of proportionality, which is very near the elastic limit.
- Be careful: some materials like rubber only obey Hooke's law for very small extensions.
It might take so time to understand this, take your time and make sure you know it as this is important in AS/A-level Physics! 👨🏫
A stretch can be elastic or plastic
Elastic:
- If a deformation is elastic, that material returns to it's original shape once forces have been removed.
- When the material is put under tension the atoms of the material are pulled apart from each other.
- Atoms can move small distances relative to their equilibrium positions with actually changing the position of the material.
- Once the load is removed, the atoms return to their equilibrium distance apart.
- For a metal, elastic deformation happens as long as Hooke's law is obeyed.
Plastic:
- If the deformation is plastic, the material is permanently stretched.
- Some atoms in the material move position relative to one another.
- When the load is removed, the atoms don't return to their original positions.
- A metal stretched past its elastic limit shows plastic deformation.
References:
https://getrevising.co.uk/revision-notes/hookes_law_2
https://www.bio-meca.com/en/glomeca-3-hookes-law/
This is the end of the topic!
Drafted by Cherry (Chemistry)