lesson
Updated 6 days ago
Water ripples move fast across a shallow tray β too fast to chase down with a simple stopwatch. How can we measure the exact speed of a moving ripple without high-tech lasers?
The Ripple Tank Setup
A ripple tank is a transparent, shallow basin of water with a motorized wooden bar that taps the surface to generate straight, parallel waves.
An overhead light shines down through the water, projecting bright and dark bands onto a white sheet below because wave crests act like mini lenses.
πA clean 2D side-view diagram of a ripple tank setup on a light gray card. At the top, an electric lamp points down. Below it sits a clear glass water tray supported on legs. A motor with a wooden oscillating dipper touches the water surface, creating wave ripples. Beneath the glass tray, light rays pass through the water to project alternating bright bands (crests) and dark bands (troughs) onto a flat white screen lying on the bench. Minimal labels with #1e2945 text: 'Overhead Lamp', 'Motor & Dipper', 'Shallow Water Tank', and 'White Card / Shadow Screen'.
Once our wave pattern is running steadily, how do we figure out how many waves are generated every single second?
Measuring Frequency
The frequency (f) is the number of complete waves passing a fixed point per second, measured in hertz (Hz).
To find it accurately, count how many wave crests pass a marked point on the screen in 10Β seconds, then divide that total count by 10.
πA visual interactive-style graphic showing frequency measurement. On the left, a digital stopwatch displays '10.0 s'. In the center, 12 wave crests travel past a red reference line marker. On the right, a calculation card displays: 'Frequency (f) = Total Waves Γ· Time' followed by 'f = 12 waves Γ· 10 s = 1.2 Hz'. Crisp typography with accent blue borders and clear high-contrast callouts.
We know how fast ripples pulse, but how can we measure the distance between waves while they are constantly moving?
Measuring Wavelength
The wavelength (Ξ») is the physical distance from one crest to the very next crest, measured in meters (m).