Idea 2of 6Builds onThe wave that stands still
Still points, widest points
Which points of the humming string never move?
Today you'll discover
- where a standing wave is perfectly still
- where it swings the widest
- the names for those two kinds of point
Think firstA string humming in two loops
The string swings in two loops. Which points move the least?
Decide first, then press Next. Watch the ringed points while the loop middles swing.
A string between two posts drawn in two loops, with small rings at the ends and the middle and a faint envelope showing the swing. After a prediction, the frames advance: the loops flip while the ringed points stay put; thin guides then mark the widest-swinging points, and both kinds are named. The last step shows three loops and asks how many widest points there are.
See the whole ideathe big idea and the key word, in one place
The big idea
Nodes stay still; antinodes swing widest.
See the patternOne loop: two nodes, one antinode. Two loops: three nodes, two antinodes. Every extra loop adds one of each.
Key words
- node
- a point of a standing wave that never moves
- antinode
- a point of a standing wave with the largest swing, halfway between nodes
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?
- Count the nodes and antinodes of a described standing wave.