Lesson Plan

• Describe why sound speed varies between solids, liquids and gases.
• Explain how stiffness (elastic modulus) and density determine the speed of sound.
• Calculate the speed of sound in a gas using the formula \(v=\sqrt{\gamma R T}\).
• Compare typical sound speeds in steel, water and air and identify the reasons for the differences.
• Identify at least two factors that modify sound speed in each state of matter.

• Projector and screen
• Whiteboard and markers
• Printed handout with speed‑of‑sound table
• Calculator worksheets
• Metal rod (solid), water container (liquid) and speaker (air demo)
• Exit‑ticket slips

Begin with a short video of a train whistle heard clearly through the rails but faint in the air to spark curiosity. Ask students what they already know about how sound travels through different materials. State that by the end of the lesson they will be able to explain why sound is fastest in solids and predict speeds in various media.

1. Do‑now (5 min): Quick quiz on wave types and prior knowledge of sound as a longitudinal wave.
2. Mini‑lecture (10 min): Introduce stiffness‑to‑density ratio, present the formulas for solids (\(v=\sqrt{E/\rho}\)) and fluids (\(v=\sqrt{K/\rho}\)), and show the comparative speed table.
3. Demonstration (10 min): Play the same tone through a metal rod and through air; discuss observed speed differences and relate to material properties.
4. Guided calculation (10 min): Students work through the example of calculating sound speed in dry air at 25 °C using \(v=\sqrt{\gamma R T}\).
5. Group activity (10 min): Using the handout, groups rank several media by speed and list factors (temperature, composition, molecular weight) that could alter each speed.
6. Check for understanding (5 min): Exit‑ticket question – “State one reason why sound travels faster in solids than in gases.”

Summarise that sound speed depends on the balance of elasticity and inertia, giving solids the highest speeds, liquids intermediate, and gases the lowest. Collect exit tickets and remind students to complete a short homework task: calculate the speed of sound in water at 15 °C using the provided bulk modulus value.