Ilka ties a rope to a post and shakes the free end. At most rhythms the rope just jiggles. At one particular rhythm, clean humps appear and swing in place: a standing wave.
Last lesson named the pattern. This lesson explains where it comes from, and why the post matters.
Every shake Ilka sends travels down the rope toward the post.
The rope's waves cannot pass the post, so each wave reflects there and travels back toward her hand.
Now two waves share the rope: the wave she keeps sending, and its reflection coming back. They are identical, and they travel in opposite directions.
Everywhere they overlap, the two waves superpose: the rope adds their displacements at each point.
At just the right shaking frequency, the sums settle into humps that swing in place.
Neither traveling wave ever stops. The standing pattern is their moment-by-moment sum.
Joby shakes a rope tied to a fence rail at just the right frequency and sees a standing wave. Name the two waves whose sum makes the pattern.
His wave travels toward the rail.
The rail reflects it, and the reflection travels back along the rope.
The wave he sends and its reflection, identical and traveling in opposite directions.
Why does the standing wave need the post?
The post sends every arriving wave back along the rope.
Without the reflection, only one wave travels the rope, and there is no second wave to superpose with.
The post supplies the reflected wave, the second of the two identical, opposite-traveling waves.
A standing wave swings on a rope tied to a wall. Which two waves sum to make the pattern?
A standing wave forms on a rope. How do the two forming waves' directions of travel compare?
Joby says: 'A standing wave is the sum of two identical waves traveling in opposite directions.' Is Joby correct?
A rope is tied to a hook on a wall. Lazlo shakes the free end at just the right frequency, and a standing wave appears. Where does the second of the two superposing waves come from?
Which pair of waves superposes to give a standing wave?
A standing wave swings on a cord. What is the pattern at each moment?