Idea 9of 9Builds onThey add, point by pointThe pattern moves, the stuff stays
The end sends it back
A crest reaches the rope's end. Then what?
Today you'll discover
- what a pulse does when the rope runs out
- why a tied end turns a crest over
- why a loose end does not
Think firstA crest runs along a rope tied to a wall
The crest reaches the tied end. What comes back along the rope?
Decide first, then press Next. Watch the end of the rope and which way the returning pulse points.
A rope running to a wall at the right, with a single crest travelling toward it. After a prediction, the frames advance: the crest reaches the tied end, turns over, and comes back as a trough; then the end is swapped for a ring on a pole and the crest comes back upright. The last step asks what returns from the bridge of a guitar string.
See the whole ideathe big idea and the key word, in one place
The big idea
A pulse reaching an end comes back. Tied: flipped. Free: upright.
Why it happensA fixed end flips the pulse because the wall pulls down exactly as hard as the crest pulls up. A free end has nothing to pull against, so it overshoots and the crest returns upright.
Key word
- reflection
- a wave returning from a boundary; at a fixed end it is inverted, at a free end it is not
About this modelThe rope is drawn as a line; the reflected pulse keeps its size, only its sign may change.
The rope is drawn as a line; the reflected pulse keeps its size, only its sign may change.
Ready to use it?
- Say whether a reflected pulse comes back inverted or upright for a described end.