Idea 1of 6Builds onThey add, point by pointThe end sends it back
The wave that stands still
A plucked string hums in place. Where is the travelling?
Today you'll discover
- what a wave and its own reflection add up to
- why the pattern breathes instead of moving along
- the name for a wave that stays put
Think firstA string between two posts, shaken into two loops
The string hums in two loops. Is there a point in the middle that never moves?
Decide first, then press Next. Watch the ringed points while everything else swings.
A string between two posts drawn in two loops, with a faint envelope showing its swing. After a prediction, the frames advance: the loops flip to the other side while small rings at the ends and the middle stay put; the whole length is then bracketed as one standing pattern. The last step shows three loops and asks how many still points lie between the posts.
See the whole ideathe big idea and the key word, in one place
The big idea
A wave and its reflection add into a standing wave.
Easy to get wrongA still point is not pinched. Two waves pass through it and happen to cancel there at every moment. It is superposition, not a clamp.
Key word
- standing wave
- the pattern formed when a wave and its reflection superpose: fixed still points and widest points, nothing travelling
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?
- Explain how a plucked string's travelling waves become a pattern that stays put.