Why does resonance cause amplitude to increase and what limits the value of maximum amplitude quora?
Answers
Because everytime you add an impulse to the system it adds "in the right way". The easiest analog is a swing. If you push the person on the swing just as they are closest to you, they will swing faster, or in other words a larger amplitude. However if you try to push them, when the swing is approaching you, you will be counteracting the movement and the swing will be moving slower and thus with a smaller amplitude.
If there was no damping in the swing the swing would move with larger and larger amplitudes (until it would make a complete revolution, but we'll ignore this possibility). However, most physical systems have damping, which limits the size of the amplitude. If you do not have damping and hit the resonance frequency, the amplitudes will go to infinity.