Differential Equation governing Simple Harmonic Motion

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Theorem

Let $B$ be a body undergoing simple harmonic motion in a straight line.

Then its motion can be described using the equation:

$\dfrac {\d^2 x} {\d x^2} = -\omega^2 x$


Proof

Consider the equation governing simple harmonic motion:

$(1): \quad x = A \map \cos {\omega t + \phi}$


Differentiating $2$ times with respect to $t$:

\(\text {(2)}: \quad\) \(\ds \dfrac {\d x} {\d t}\) \(=\) \(\ds -\omega A \map \sin {\omega t + \phi}\) Derivative of Cosine Function
\(\text {(3)}: \quad\) \(\ds \dfrac {\d^2 x} {\d t^2}\) \(=\) \(\ds -\omega^2 A \map \cos {\omega t + \phi}\) Derivative of Sine Function
\(\ds \) \(=\) \(\ds -\omega^2 x\)

We have arrived at a ordinary differential equation of order $2$:

$\dfrac {\d^2 x} {\d t^2} = -\omega^2 x$

$\blacksquare$


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