Attaching a water hose sprinkler to a speaker
Functions & Equations
A vibrating speaker with a water hose taped to it turns a stream of droplets into a pattern that seems to freeze or crawl — model why.
Introduction
Tape a running hose to a speaker cone and play a tone through it: the water breaks into droplets at the speaker's frequency, and under the right conditions the stream of drops can look frozen, or slowly crawling forwards or backwards, even though the water is actually falling at normal speed. This is the same strobe effect that makes wagon wheels appear to spin backwards in old films, driven here by the vibration frequency instead of a camera shutter. You can model the droplet stream as a sine wave and use that model to explain what a viewer's eye, or a phone camera, actually sees.
Guiding Questions
- Water from a vibrating hose appears frozen or crawling on camera. What two frequencies are interacting?
- Model the water stream's shape as a wave and explain the strobe-like camera effect.
- Reproduce the experiment. Which speaker frequencies give frozen, forward and backward effects with your camera?
- Predict the apparent motion for a frequency you haven't tried, then test the prediction.