Simple Harmonic Motion (SHM) is defined by the governing equation: $a=-{\omega }^{2}x$ where:

• $a$: instantaneous acceleration
• $x$: displacement from the equilibrium position
• $\omega$: angular frequency The negative sign indicates that the acceleration (and thus the restoring force $F=ma$) is always directed towards the equilibrium position, which is opposite to the direction of displacement.