Study Notes
Elastic and plastic behaviour describes how materials respond to external forces, either returning to their original shape or undergoing permanent deformation.
- Elastic Deformation — temporary shape change that is reversible when the force is removed. Example: A rubber band stretching and returning to its original shape.
- Plastic Deformation — permanent shape change that is irreversible when the force is removed. Example: A bent metal rod that does not return to its original shape.
- Elastic Limit — the maximum extent to which a material can be deformed elastically. Example: The point on a force-extension graph where the material stops behaving elastically.
- Brittle Materials — materials that break without significant plastic deformation. Example: Glass shattering when hit.
- Ductile Materials — materials that can undergo significant plastic deformation before breaking. Example: Copper wire stretching before snapping.
- Elastic Potential Energy — stored energy in a material when it is stretched or compressed. Example: Energy stored in a compressed spring.
Exam Tips
Key Definitions to Remember
- Elastic Deformation: Temporary and reversible shape change.
- Plastic Deformation: Permanent and irreversible shape change.
- Elastic Limit: Maximum extent of elastic behaviour.
- Elastic Potential Energy: Energy stored in a deformed material.
Common Confusions
- Confusing elastic and plastic deformation as the same.
- Misunderstanding the elastic limit as the breaking point.
Typical Exam Questions
- What is elastic deformation? Temporary shape change that is reversible.
- What happens when a material exceeds its elastic limit? It undergoes plastic deformation and does not return to its original shape.
- How is elastic potential energy calculated? Using the formula 1/2 * k * x^2 for materials obeying Hooke's Law.
What Examiners Usually Test
- Understanding of force-extension graphs.
- Differences between brittle and ductile materials.
- Calculation and interpretation of elastic potential energy.