Lesson Plan

• Recall the formula EP = ½Fx = ½kx² and the conditions for its use.
• Explain the concepts of stress, strain, limit of proportionality, elastic limit and plastic region.
• Apply Hooke’s law and the energy‑storage formula to calculate force, spring constant and elastic potential energy for a material deformed within its linear region.
• Analyse a stress‑strain diagram to identify the elastic and plastic zones.
• Identify common misconceptions about elastic deformation.

• Projector or interactive whiteboard
• Slide set with stress‑strain diagram
• Worksheet with example problem and calculation space
• Spring or elastic band for a quick demonstration
• Rulers/measuring tapes
• Calculator or classroom computers

Begin with a quick demonstration stretching a spring to show how the force increases linearly, prompting students to predict the energy stored. Review prior knowledge of stress, strain and Hooke’s law, emphasizing that today’s focus is on the limit of proportionality. State the success criteria: students will be able to recall the EP formula, distinguish elastic from plastic behaviour, and solve numerical problems using the formula.

1. Do‑now (5’) – Students complete a short quiz on stress, strain and Hooke’s law on the worksheet.
2. Mini‑lecture (10’) – Present the EP = ½Fx = ½kx² derivation and discuss the limit of proportionality using the slides.
3. Demonstration (5’) – Stretch a spring in front of class, plot force vs. extension on the board, and highlight the linear region.
4. Guided practice (15’) – Work through the steel‑wire example together, filling a table of k, F and EP.
5. Independent practice (10’) – Students solve a similar problem on their worksheet while the teacher circulates.
6. Check for understanding (5’) – Quick exit tickets: write the condition required for using EP = ½kx².

Summarise that elastic potential energy is stored only while deformation stays within the limit of proportionality and that the area under the linear part of the stress‑strain curve represents this energy. Ask a few students to share their exit‑ticket answers to reinforce the criteria. Assign homework: complete a set of three problems involving different materials and indicate whether the deformation is elastic or plastic.