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Lesson: Chapter 4 — Waves and their applications

4.1.2. Longitudinal waves 1 of 3

Compressions and rarefactions

Push and pull the slinky along its own length instead of shaking it sideways, and a different kind of wave runs along it: a longitudinal wave.

Activity 4.3

You will need: a slinky, a piece of ribbon

  • Lay a slinky on a table and fix one end to the table.
  • Tie a piece of ribbon to one coil.
  • Move the other end forwards and backwards by hand, along the slinky.

Figure to be added

Figure 4.9 — a slinky pushed and pulled along its length, showing bunched-up coils (compressions) and spread-out coils (rarefactions), a ribbon on one coil, and the direction of energy transfer.

The observation

Pushing the free end forwards squeezes the coils there together. Pulling it back spreads them apart. The squeezed and spread regions travel along the slinky, and the ribbon moves forwards and backwards about one place.

Compression

A region where the coils are squeezed close together.

Rarefaction

A region where the coils are spread further apart.

Longitudinal wave

If the particles of the medium vibrate parallel to the direction the wave travels, the wave is called a longitudinal wave.