Resonance is a phenomenon that occurs when an external force drives a system at its natural frequency—the specific frequency at which the system tends to vibrate on its own. When this happens, the system absorbs energy efficiently from the driving force, leading to large amplitude oscillations.
Every physical system—like a swing, a guitar string, or a building—has one or more natural frequencies. If energy is applied at just the right rate (matching the natural frequency), even a small, repeated force can build up large vibrations over time. This is resonance.
A classic example is pushing a child on a swing: if you push at the right rhythm (matching the swing’s natural motion), the swing goes higher with each push. However, resonance can also be dangerous—such as in bridges or buildings—if external forces like wind or earthquakes match their natural frequencies, potentially leading to structural failure.
Engineers must consider resonance to either harness it (like in musical instruments) or avoid it (as in architecture or machinery).