The damped natural frequency fd is related to the natural frequency fn by a relation
where damping ratio is <= 1
so the fd is less than the natural frequency
When a satellite revolves around a planet in its orbit, it possesses both potential energy (due to its position against the gravitational pull of earth) and kinetic energy (due to orbital motion).
Hence we can say that total energy of circularly orbiting satellite is negative.
instantaneous acceleration is measured over a "short" time interval. The word short in this context means infinitely small or infinitesimal — having no duration or extent whatsoever.
It's a mathematical ideal that can can only be realized as a limit. The limit of a rate as the denominator approaches zero is called a derivative.
Instantaneous acceleration is then the limit of average acceleration as the time interval approaches zero — or alternatively, acceleration is the derivative of velocity.
M is mutual inductance