Idea 7of 9Builds onThe pattern moves, the stuff staysHow tall
They add, point by point
Two crests meet on a rope. Crash, bounce, or what?
Today you'll discover
- what two pulses do when they meet
- what the rope does at every point
- what each pulse looks like afterward
Think firstTwo 1 cm crests head toward each other
Two crests, each 1 cm tall, meet on a rope. When they overlap, how tall is the rope?
Predict first, then press Next. Watch the bottom line, the rope itself.
Three rows: a pulse travelling right, a pulse travelling left, and the rope itself beneath them. After a prediction, the frames advance: the pulses move toward each other and, where they overlap, the rope's line is the two heights added, twice as tall. Afterward each pulse continues unchanged. The last step meets a crest with a trough and asks what the rope does.
See the whole ideathe big idea and the key word, in one place
The big idea
Overlapping waves add, point by point, then walk on unchanged.
Easy to get wrongPulses are not objects. They cannot collide or bounce. Where they overlap the rope simply shows their sum, and afterward each is exactly as it was.
Key word
- superposition
- the principle that overlapping waves add: the medium's displacement is the sum of the individual displacements at each point
About this modelThe pulses never bounce. They add while they overlap, then walk on unchanged.
The pulses never bounce. They add while they overlap, then walk on unchanged.
Ready to use it?
- Draw or describe the rope where two given pulses overlap, and what remains afterward.