The natural frequency is the frequency at which a system vibrates when disturbed. A vibrating object may have one or multiple natural frequencies. All objects vibrate when acted on by an external stimulus. The vibrations occur at various natural frequencies and with varying shapes. The modal frequency and the modal shape, together, characterize a vibration mode.
The natural frequency of a system can be altered by changing the properties of the system. For example, a tuning fork for the musical note "A" vibrates at a frequency of 440 Hz. To change the natural frequency you can change, for example, the length of the two tines. Similarly, you can change the length, thickness, or tension of a guitar string to change its natural frequency.
In a modal frequencies analysis, the natural frequencies of all calculated modes are listed in the Mode dropdown above the legend. Each entry shows the mode number and frequency in Hertz (Hz), for example Mode 1: 440 Hz. The number of modes that the solver calculates depends on the study settings you choose when setting up the simulation.
When you select a mode from the dropdown, the displacement plot updates to show the deformed shape for that vibration mode.