Resonance?

Question

Can someone concisely explain to me what resonance is in physics (in wave theory)?

Answer 1

Darn good question.
First let's look at a pendulum
T=2 pi sqrt(L/g)
T- period of oscillation
pi - 3.14...
sqrt - square root
L - length of a string
g - gravitational acceleration (9.81m/s^2 )

I want you to notice that the period of the oscillation is defined by the physical property of the object namely the length of the string that makes the pendulum.
As you know the frequency is f=1/T. In our case it is the so called natural frequency. Natural to that particular pendulum or object. The same idea is true with other objects as well that may not necessary be pendulums but can be a box, a building or a bridge.

Wiki gives a good definition of a resonance :” In physics, resonance is the tendency of a system to oscillate at maximum amplitude at a certain frequency. This frequency is known as the system's natural frequency of vibration, resonant frequency...”