Waves transfer energy from one place to another without transporting matter overall. The key difference between transverse and longitudinal waves is the direction of particle oscillation compared with the direction the wave travels. In a transverse wave, particles move perpendicular to the direction of propagation.
In a longitudinal wave, particles move parallel to the direction of propagation.
Key Facts
- Wave speed equation: v = fλ, where v is speed, f is frequency, and λ is wavelength.
- Transverse wave motion: particle oscillation is perpendicular to wave propagation.
- Longitudinal wave motion: particle oscillation is parallel to wave propagation.
- In a transverse wave, amplitude is the maximum displacement from the equilibrium position.
- In a longitudinal wave, wavelength is the distance between neighboring compressions or neighboring rarefactions.
- Examples: light and waves on a string are transverse, while sound in air is longitudinal.
Vocabulary
- Transverse wave
- A wave in which particles of the medium oscillate perpendicular to the direction the wave travels.
- Longitudinal wave
- A wave in which particles of the medium oscillate parallel to the direction the wave travels.
- Propagation
- The motion of a wave as energy spreads through space or through a medium.
- Compression
- A region in a longitudinal wave where particles are crowded closer together than normal.
- Rarefaction
- A region in a longitudinal wave where particles are spread farther apart than normal.
Common Mistakes to Avoid
- Confusing particle motion with wave motion is wrong because particles in a medium usually oscillate around fixed positions while the wave pattern and energy travel forward.
- Calling all waves transverse is wrong because sound in air and many waves in springs are longitudinal, with motion parallel to propagation.
- Measuring wavelength from a compression to a rarefaction is wrong because one full longitudinal wavelength is compression to compression or rarefaction to rarefaction.
- Assuming amplitude changes wave speed is wrong in many basic wave models because speed is determined mainly by the medium, such as tension and mass density for a string or elasticity and density for sound.
Practice Questions
- 1 A transverse wave on a rope has a frequency of 5.0 Hz and a wavelength of 2.0 m. What is its wave speed?
- 2 A sound wave in air travels at 340 m/s and has a frequency of 680 Hz. What is its wavelength?
- 3 A student watches a slinky wave travel to the right while the coils move back and forth to the left and right. Is the wave transverse or longitudinal, and how can you tell?