Waves Study Guide

Waves are disturbances that transfer energy without transferring matter. They can be categorised based on the direction of oscillation of the particles of the medium relative to the direction of energy transfer. In transverse waves, the oscillations are perpendicular to the direction of energy transfer. Imagine a rope tied at one end: if you flick it up and down, the wave travels along the rope, but the rope segments move up and down, at right angles to the wave's movement. Examples include electromagnetic waves (like light), all types of seismic S-waves, and ripples on water surfaces. Longitudinal waves, on the other hand, feature oscillations that are parallel to the direction of energy transfer. Think of a Slinky spring pushed and pulled along its length; compressions and rarefactions travel along the spring, and the spring coils move back and forth in the same direction as the wave's travel. Sound waves and seismic P-waves are classic examples of longitudinal waves. Water waves are particularly interesting because although surface ripples are often approximated as transverse, deep-water waves involve particle motion that is a combination of both, tracing circular or elliptical paths.

When a wave pulse is sent from a source, travels to a reflector, and returns, you can calculate the depth or distance to the reflector using the wave speed and the total time measured. The core formula is: depth (or distance to reflector) = (wave speed × round-trip time) / 2. This accounts for the wave traveling to the reflector and back (so, twice the actual one-way distance). This principle allows accurate measurement in applications such as sonar and seismic surveys, where knowing precise wave speeds and measuring round-trip times lets you deduce the depth or distance to a target or boundary.