Demos: 1S-16 Columbia Wave Machine
This antique demo is a classic. Three rows of circular disks are linked to a common shaft which can be cranked from the back by hand. The linking is so arranged that one row of disks simulates transverse waves, another simulates longitudinal waves, and one which combines the latter two motions to simulate rolling water waves. Each of these can be displayed separately by the closing and opening of the appropriate doors.
Directions: Start with the set of disks labeled ether waves, which simulate the transverse wave motion. Turn the crank at a reasonable speed to show the up and down motion of the disks. Then swing the bottom door upward to hide this mode and at the same time uncover the set of disks labeled sound waves, or the longitudinal mode. Finally, swing the upper door down to reveal the set of disks labeled water waves.
Suggestions for Presentation: A little flair doesnt hurt here. What do we have behind Door No. 1? Have the students focus their attention on the motion of the disks. Point out the up and down motion of the transverse wave and the back-and-forth motion of the longitudinal wave. Ask if either of these represents what happens in a water wave, as in ocean waves. Students will likely suggest the transverse wave, but ask if there is something about the wave that doesnt quite look right. Then open the final door and show the rolling motion, which most students will agree looks more like an ocean wave. Point out that this is a combination of the two types of waves. Further suggest that a cork floating on the water would execute not an up and down motion, but rather a circular (or elliptical, depending on water conditions) motion.
Applications: Various types of waves in media. Ocean waves. In the latter, the rolling motion simulates to some extent the breaking of waves and undertow.