Materials:

• Longitudinal Wave Apparatus (stored above glassware)

Instructions:

To demonstrate the oscillatory motion of longitudinal waves, simply disrupt or pulse the apparatus such that you stretch or contract the small springs. The waves will travel down the spring demonstrating the expansion and contraction of longitudinal wave motion.

Explanation:

Much like ocean waves and light waves, longitudinal waves propagate through mediums with a wavelength, velocity, and frequency. Thus they follow the fundamental formula:

Which verifies their wavelike behavior. Longitudinal waves propagate through mediums by expansion and contraction of particle densities. Just as transverse waves have both nodes and antinodes as peaks or troughs, longitudinal waves have nodes and antinodes defined by regions of constant density (nodes) and regions of alternating high and low density (antinodes), as seen in Figure 1. The areas of high & low density are known as compressions and rarefactions, respectively.

Figure 1: Displaying the differences between two in-phase waves of longitudinal (lower) and transverse (upper) nature

Sound waves are a great example of a longitudinal wave, as they move through a medium of particles creating compressions and rarefactions. The reason there is no sound in outer space is because it is a vacuum and has no medium through which the wave can propagate.

Sound waves also travel parallel with their direction of energy transfer (denoted in Figure 1), as opposed to transverse waves whose oscillations are perpendicular to their direction of energy transfer. This is one of the key difference between the two types of waves.

A slinky can act as a medium that demonstrates longitudinal wave motion, as seen by the orange longitudinal wave in Figure 1. This demonstration has two slinkies attached to multiple vertical ribs. As one slinky compresses, the other extends. Causing a wave to propagate with down the length of the ribs.

Notes:

• Reasonably heavy & doesn’t fit on carts. Should be carried to classes if can be.

Written by Phoenix Gallagher