#### Extracting Physical Quantities

Since we are using a force-wave simulation, the state variable (delay element output) is in units of physical force (newtons). Specifically, . (The physical force is, of course, 0, while its traveling-wave components are not 0 unless the mass is at rest.) Using the fundamental relations relating traveling force and velocity waves

where here, it is easy to convert the state variable to other physical units, as we now demonstrate.

The velocity of the mass, for example, is given by

The kinetic energy of the mass is given by

*I.e.*, the square of the state variable can be scaled by to produce the physical kinetic energy associated with the mass.

**Next Section:**

A More Formal Derivation of the Wave Digital Force-Driven Mass

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Series Reflection Free Port