ABSTRACT
We could solve this using a separate force = mass * acceleration term for each mass. There are some problems with Figure 9.1 as drawn, however. One problem is that the masses are free to move side-to-side as well as up and down. This is called longitudinal motion, and it doesn’t usually happen with actual strings under tension. If it does, it isn’t nearly as important as the up and down transverse motion. We could restrict the mass-spring system as shown in Figure 9.2, placing each mass on a frictionless guide rod so that the masses could only move up and down.
