Idea 3of 6Builds onStill points, widest pointsThe medium sets the speed
Only the fits survive
Why does a string play notes, not noise?
Today you'll discover
- what every loop is, in wavelengths
- which wavelengths a fixed length allows
- why a shorter string plays higher
Think firstA 1 m string hums in one loop
You press the string shorter and pluck again. What happens to the note?
Decide first, then press Next. Count the loops and read the bracket under one of them.
A one-metre string between two posts drawn in one loop, with a bracket under the loop and a bracket along the full length. After a prediction, the loop's bracket is labelled as half a wavelength, then the string is redrawn in two loops and three loops with the brackets relabelled. The last step presses the string to half its length and asks for the new fundamental.
See the whole ideathe big idea and the key word, in one place
The big idea
Only whole half-wavelengths fit: L = n λ ÷ 2.
Compare themShorter string: shorter wavelength, higher note. Not quieter, not lower. The speed on the string never changed.
Key words
- harmonic
- one of the standing-wave patterns that fit a length: the nth harmonic has n loops and n times the fundamental's frequency
- fundamental
- the lowest-frequency standing wave that fits: one loop on a string fixed at both ends, L = λ ÷ 2
About this modelOnly wavelengths that fit the length survive; the rest cancel within a few reflections.
Only wavelengths that fit the length survive; the rest cancel within a few reflections.
Ready to use it?
- Find the wavelength and frequency of a given harmonic on a string of known length and wave speed.