Waves & Optics · 01 / 06

Wave Motion

A traveling wave carries a changing pattern and transfers energy through space. In a mechanical wave, the medium's particles usually oscillate around equilibrium rather than traveling with the wave itself.

The learner question

What actually moves when a wave travels?

The wave pattern moves with a propagation speed. For a transverse mechanical wave, individual particles move up and down locally while the crest pattern advances horizontally.

Core relationships
v=fλv=f\lambda
y=Asin(kxωt)y=A\sin(kx-\omega t)

Amplitude controls displacement scale; frequency and wavelength combine with speed.

Traveling-wave lab

Change the wave and keep every representation synchronized.

phase = 54°
λpropagation →
wavelength λ
2.00 m
frequency f
1.50 Hz
period T
0.67 s
Amplitude A1.00 m
Frequency f1.50 Hz
Wave speed v3.00 m/s
Phase0.15 cycle
wave idea
The pattern propagates

A crest at one location is replaced by another crest later. Tracking equal phase points reveals the wave speed.

wave idea
The medium oscillates locally

In this transverse model, sample particles move perpendicular to propagation. They do not ride the crest across the whole domain.

wave idea
Changing frequency changes wavelength at fixed speed

If the medium fixes wave speed, increasing frequency packs more cycles into the same distance, so wavelength decreases.

Amplitude
AA

Maximum displacement from equilibrium in this wave variable. Larger amplitude changes the scale, not the wavelength.

Wavelength
lambda\\lambda

Spatial repeat distance between equal-phase points such as neighboring crests.

Frequency
ff

Number of oscillation cycles per second at one location. Period is its reciprocal.

Transfer check

A wave travels through a medium at constant speed. Its frequency doubles. What happens to its wavelength?

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