6.2 Mechanical Waves

Transverse vs. Longitudinal Waves

Mechanical waves transfer energy through a medium without transferring matter. In transverse waves (e.g., waves on a string), particle motion is perpendicular to wave travel. In longitudinal waves (e.g., sound), particle motion is parallel to wave travel, creating compressions and rarefactions.

Wave Properties: v, f, λ, A

Wavelength (λ) is the distance between repeating points; frequency (f) is cycles per second; period (T) = 1/f. Wave speed v = fλ depends on the medium's properties (tension, density), not on amplitude or frequency. Amplitude determines energy/intensity but not speed.

Superposition and Standing Waves

When waves overlap, displacements add via superposition, causing constructive or destructive interference. Waves confined between boundaries can form standing waves with fixed nodes (no displacement) and antinodes (max displacement), determined by boundary conditions and wavelength.

Key terms

Transverse wave

A wave where particle motion is perpendicular to the direction of wave travel (e.g., string waves).

Longitudinal wave

A wave where particle motion is parallel to the direction of wave travel, creating compressions and rarefactions (e.g., sound).

v = fλ

Wave speed equals frequency times wavelength; speed depends on the medium, not amplitude or frequency.

Superposition

Principle that overlapping waves add their displacements, producing constructive or destructive interference.

Node vs. Antinode

Node: point of zero displacement in a standing wave. Antinode: point of maximum displacement.

Try an AP-style question

In a longitudinal wave, how do particles of the medium move?

1. Parallel to the direction of wave travel
2. Perpendicular to the direction of travel
3. In circles
4. They don't move