Question

what do you understand by natural frequency or normal mode of vibration

Answer 1

$\mathsf{}$A stretched string or an air column in a closed tube open tube vibrates with definite set of frequencies called as normal mode of oscillations. Each of these frequencies is a resonant frequency of the system. The lowest frequency is the fundamental mode or first harmonic

Answer 2

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A normal mode of an oscillating system is a pattern of motion in which all parts of the system move sinusoidally with the same frequency and with a fixed phase relation. These fixed of frequencies the normal modes of a system are known as its natural frequencies or resonant frequencies.

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