Wave properties (amplitude, wavelength, frequency)
The idea
A wave is a traveling disturbance that carries energy from one place to another without carrying the material along with it. Watch a buoy when a wave passes: the buoy bobs up and down, but it does not surf to shore — the water mostly stays put while the energy moves on. You have felt this with vibrations making sound. Three numbers describe any wave: amplitude (how far it swings from rest, which sets how much energy it carries), wavelength (the distance from one crest to the next), and frequency (how many complete waves pass per second, measured in hertz, Hz).
These pieces connect through one tidy rule: wave speed = frequency × wavelength. The misconception to avoid is thinking you can make a wave travel faster by shaking the source harder or faster. Cranking up amplitude makes a taller wave; cranking up frequency packs the crests closer together (shorter wavelength); but the SPEED is set by the medium the wave travels through — water depth, string tension, the air itself. Frequency and wavelength trade off so their product, the speed, stays put.
Worked example
A buoy bobs up and down once every 4 s as ocean waves pass, and the crests are 8 m apart. How fast are the waves traveling?
- One full wave passes every 4 s, so the frequency is 1 ÷ 4 = 0.25 Hz — a quarter of a wave each second.
- Apply the wave equation: speed = frequency × wavelength = 0.25 Hz × 8 m = 2 m/s.
- Cross-check with plain reasoning: a whole 8 m wavelength slides past in 4 s, and 8 m ÷ 4 s = 2 m/s. Both routes agree.
- Interpret what would NOT change this: taller waves (bigger amplitude) would pound the buoy harder but still travel at 2 m/s — the medium, not the wave's size, sets the speed.
Answer. The waves travel at 2 m/s across the water.
Check your understanding
- Why does increasing a wave's frequency shorten its wavelength instead of speeding the wave up?
- Which property of a wave would you change to make it carry more energy, and what would that look like on water?
- How would you measure the frequency, wavelength, and speed of ripples in a bathtub using only a ruler and a stopwatch?
- If a wave crosses from deep water into shallow water and slows down, what must happen to its wavelength, and why?
Build the foundations first
Wave properties (amplitude, wavelength, frequency) builds on these concepts. If any feel shaky, start there.