An experiment is set up with a loudspeaker positioned at the left end of a horizontal glass tube containing air. The loudspeaker produces a progressive sound wave that propagates horizontally from left to right through the tube. A lightweight bead is suspended in the air inside the tube, as shown in the diagram below.
Which of the following statements correctly describes the motion of the suspended bead as the sound wave passes it?
It oscillates horizontally, left and right, about a fixed equilibrium position.
It oscillates vertically, up and down, about a fixed equilibrium position.
It is carried continuously to the right along the length of the tube.
It remains completely stationary.