Normal modes refer to the oscillatory patterns or vibrations of a system at its natural frequency. These modes occur when all parts of the system vibrate at the same frequency and are in phase with each other.
Propagation modes, also known as wave modes, refer to the different ways in which waves can travel through a medium. These modes are determined by the physical properties of the medium, such as density and elasticity.
The main difference between normal modes and propagation modes is that normal modes refer to the oscillatory behavior of a single system, while propagation modes refer to the behavior of waves traveling through a medium.
Normal modes and propagation modes are related in the sense that the natural frequency of a system's normal modes can determine the type of propagation modes that can occur in that system. For example, a system with a low natural frequency will only allow for low frequency propagation modes.
Yes, normal modes and propagation modes can coexist in a system. In fact, the propagation of waves through a medium can be thought of as a superposition of multiple normal modes. This allows for more complex and diverse wave behavior in a system.