To measure the amplitude of a longitudinal wave, you focus on the maximum displacement of particles from their equilibrium position along the direction of wave propagation.

How to Measure Amplitude of a Longitudinal Wave

• Identify the equilibrium position : This is the undisturbed position of the particles in the medium before the wave passes.
• Measure maximum displacement : Track a specific particle or point in the medium (for example, a marked spot on a slinky) and observe how far it moves from the equilibrium position during the wave cycle.
• Amplitude is the maximum displacement from equilibrium : It is the distance between the equilibrium position and the point of maximum compression or rarefaction (the densest or least dense part of the medium)

For example, in a slinky demonstration, if a marked point moves between 40 cm and 60 cm on a meter stick, the amplitude is the distance from the midpoint (50 cm) to one of these extremes (10 cm in this case)

Additional Notes

• The amplitude corresponds to the difference in density or pressure from the undisturbed state to the maximum compression in the wave

• If you have a graph of pressure or density versus time or position, amplitude can be measured as the difference between the equilibrium pressure and the peak pressure of compression or rarefaction

• The amplitude indicates the wave's energy: larger amplitude means more energy carried by the wave

In summary, the amplitude of a longitudinal wave is measured by determining the maximum displacement of particles from their rest position along the wave direction, which can be done by direct observation of particle motion or by analyzing pressure/density variations graphically.