The best way to set a child's swing in motion is to give it small pushes in time with the natural period of the swing. This is an example of a general principal in physics called resonance.
Resonance is said to occur whenever a particular body or system is set into oscillation at its own natural frequency as a result of impulses received from some other system which is vibrating with the same frequency.
Fig. 1.23 Effect of the frequency of the forced vibration on amplitude
Under these conditions it is possible for a very large amplitude of vibrations to be set up.
We find applications of the same principle in other branches of ...