Beats and Resonance in Forced Undamped Vibration

This applet shows the solution of a forced undamped spring-mass system: $m y'' + k y = F_0 \cos (\omega t)$ with initial conditions $\,y(0) = 0$, $\,y'(0)=0$. The blue vertical lines are at one second intervals. The angular frequency $\omega$ of the forcing term can be adjusted (between 40 and 70) by using the slider, or by typing a number in the box at bottom right and pressing Enter.