Commons

f / As the wave pattern passes the rubber duck, the duck stays put.The water isn’t moving forward with the wave.g / As the wave pulse goesby, the ribbon tied to the springis not carried along. The motionof the wave pattern is to theright, but the medium (spring) ismoving up and down, not to theright.2. The medium is not transported with the wave.Figure f shows a series of water waves before it has reached arubber duck (left), having just passed the duck (middle) and havingprogressed about a meter beyond the duck (right). The duck bobsaround its initial position, but is not carried along with the wave.This shows that the water itself does not flow outward with thewave. If it did, we could empty one end of a swimming pool simplyby kicking up waves! We must distinguish between the motion ofthe medium (water in this case) and the motion of the wave patternthrough the medium. The medium vibrates; the wave progressesthrough space.self-check AIn figure g, you can detect the side-to-side motion of the spring becausethe spring appears blurry. At a certain instant, represented by a singlephoto, how would you describe the motion of the different parts of thespring? Other than the flat parts, do any parts of the spring have zerovelocity? ⊲ Answer, p. 182A worm example 2The worm in the figure is moving to the right. The wave pattern,a pulse consisting of a compressed area of its body, moves tothe left. In other words, the motion of the wave pattern is in theopposite direction compared to the motion of the medium.168 Chapter 8 Waves