Resonant frequency is the natural frequency at which an object or system vibrates when it is disturbed. When an external force matches this frequency, the object can oscillate with greater amplitude, leading to increased energy transfer. This phenomenon is observed in various systems, such as musical instruments, bridges, and even buildings. For example, a guitar string vibrates at specific frequencies to produce musical notes. If a singer hits the right pitch, their voice can cause the string to resonate, amplifying the sound. Understanding resonant frequency is crucial in engineering to prevent structural failures, such as those caused by earthquakes.