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 $2$:
- $\dfrac {\d^2 x} {\d t^2} = -\omega^2 x$
$\blacksquare$
Sources
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): harmonic motion
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): harmonic motion