Resonance- sound Can someone please explain resonance to me? I thought it was when an external object has the same frequency as an object, so through constructive interference, the amplitude is intensified. And maybe this has something to do with standing waves, I don't know. But can someone please further explain this? Thanks. 
 A: Resonance is a property that some systems exhibit due to their specific structure, but fundamentally involves the trapping and a structural means by which energy can flow within the system between different states of energy.
The trapping of energy means that the system structure enables the system to admit at least as much energy as what energy is lost by the system. And the flow between internal states means that energy at some times may exist as potential energy and at other times as kinetic energy, or in other types of systems as electrical and magnetic fields.
Resonant systems are defined as having modes or natural frequencies and these are states of internal energy flow at which there is little energy loss relative to energy intake. Some resonant systems reach an equilibrium of energy flow and maintain a steady resonant state, but others may take in more energy than what can be lost, and in this case may reach a structural limit with regards to how much energy they can contain which can cause the system to break. A classic example is the Tacoma Narrows bridge collapse which was a mechanical resonance of the bridge structure driven by aeroelastic flutter.
Resonance exists in all types of systems, mechanical electrical, geophysical, etc., natural as well as man made systems and at all scales from within the nucleus of the atom to galactic structures. At human scales resonance can be used to our advantage or can lead to destructive events. Resonance is all around us.
