### 1.2 Definitions, equations and graphs

### 1.2.1 Definition of Simple Harmonic Motion (SHM): LO (d)

A motion where the acceleration a of an object is always directed towards a fixed point ( the equilibrium position O ) and proportional to its displacement x from the fixed point is said to be be simple harmonic.

Defining equation of SHM

a = - ω2 x

Observe from the model or the animation, suggest the reason for the negative sign.

The negative sign means a is always directed towards the equilibrium point while x is pointing away from equilibrium point O.
In other words a and x are in the opposite direction.

### 1.2.1.1 Model:

1. Run Sim
2. http://iwant2study.org/ospsg/index.php/70