Lesson Plan

• Describe how compressions and rarefactions create a longitudinal sound wave.
• Explain the link between pressure, density and particle motion in compressions and rarefactions.
• Apply the wave equation v = fλ to relate frequency, wavelength and speed of sound for these regions.
• Compare everyday examples that illustrate compressions and rarefactions.
• Analyse a diagram of a longitudinal wave to identify compression and rarefaction zones.

• Projector and laptop with animation
• Speaker or tuning‑fork for demonstration
• Printed worksheet containing a longitudinal wave diagram
• Clickers or quiz cards for formative checks
• Ruler/scale for wavelength calculations
• Whiteboard and markers

Begin with a short video of a musical instrument and ask students how sound travels from the instrument to our ears. Review the difference between transverse and longitudinal waves that they studied last week. Explain that by the end of the lesson they will be able to describe and diagram the compressions and rarefactions that make up a sound wave.

1. Do‑Now (5 min): Quick written recall of wave types and particle motion.
2. Mini‑lecture with animation (10 min): Define compression and rarefaction, show the side‑view diagram and link to pressure/density changes.
3. Demonstration (8 min): Use a tuning‑fork in water to visualise compressions and rarefactions.
4. Guided worksheet activity (12 min): Students label a diagram, calculate wavelength using v = fλ, and answer short questions.
5. Interactive quiz (5 min): Clicker questions to check misconceptions about pressure and density.
6. Summary discussion (5 min): Students verbally summarise the key characteristics of compressions and rarefactions.

Recap the alternating pattern of high‑pressure compressions and low‑pressure rarefactions and how they travel as a longitudinal wave. Ask each student to write one‑sentence exit ticket describing why compressions are essential for sound transmission. For homework, students will find an everyday sound source, sketch its longitudinal wave, and label the compression and rarefaction regions.