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## Pressure Wave Simulation: Instructor's Guide

### Main Ideas

• Relationship between voltage and charge
• Relationship between pressure and displacement waves
• Reflection and transmission coefficients
• Sinusoidal functions

Estimated Time: 5 minutes

Students are presented with a picture of molecules at three successive times and asked to draw both the displacement and pressure graph that would represent the picture. A Mathematica simulation of the situation is used to summarize the discussion.

### Prerequisite Knowledge

• Sinusoidal functions.
• Derivative relationship between pressure and displacement

### Props/Equipment

• Small White Boards
• Computer with Mathematica

### Activity: Introduction

This activity begins with a SWBQ where students are presented with a picture of molecules of molecules at three successive times and asked to draw both the displacement and pressure graph that would represent the picture. ### Activity: Student Conversations

• What are the dots? – there are several analogies to help the students think about what the dots represent:
• What kind of a wave is this? – answers such as longitudinal and traveling can lead to good conversation.

### Activity: Wrap-up

Things to emphasize in the discussion:

• the connection of displacement, force, and pressure to charge, current, and voltage,
• the derivative a sinusoidal function is itself a sinusoidal function and also satisfies the wave equation and have reflection and transmission coefficients,
• the sign difference between the reflection and transmission coefficients for displacement and pressure waves,

### Extensions

This is a good follow-up activity to the Creating a Pressure-like wave in a Coaxial Cable kinesthetic activity.

Together, these two activities provide an excellent set up for the Wave Propagation in a Coaxial Cable lab.

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