Overview
This lecture explains the differences between elastic and inelastic deformation, how to calculate the force needed to stretch or compress elastic materials, and the related energy transfers during these processes.
Elastic and Inelastic Deformation
- Elastic materials return to their original shape when the applied forces are removed.
- Elastic deformation occurs when an object changes shape or length and then returns to its original form after the forces are gone.
- More than one force must be applied to change an object's shape or length; otherwise, the object just moves.
- Inelastic materials do not return to their original shape after forces are removed (inelastic deformation).
Calculating Force for Stretching or Compression
- The force required to stretch or compress an elastic object is calculated using: Force (N) = spring constant (N/m) × extension or compression (m).
- This formula is not given in exams and must be memorized.
- Example: To extend a spring by 0.04 m with a spring constant of 200 N/m, the force needed is 8 N.
- The same equation applies for both stretching (extension) and squeezing (compression).
Energy Transfers in Elastic Objects
- When an elastic object is stretched or compressed, work is done and elastic potential energy is stored in the object.
- The work done equals the elastic potential energy if the object does not undergo inelastic deformation.
Key Terms & Definitions
- Elastic Material — A material that returns to its original shape when forces are removed.
- Elastic Deformation — Change in shape or length of an object that is reversible after removing forces.
- Inelastic Material — A material that does not return to its original shape after forces are removed.
- Inelastic Deformation — Irreversible change in shape or length of an object due to applied forces.
- Spring Constant — A measure (in N/m) of how stiff a spring or elastic object is.
- Elastic Potential Energy — Energy stored in an object when it is deformed elastically.
Action Items / Next Steps
- Memorize the force calculation formula: Force = spring constant × extension (or compression).
- Review the video on elastic potential energy from the energy topic.
- Prepare for the next class on the required practical: stretching a spring.
- Practice questions on forces and elasticity in the vision workbook.