Jean Le Rond d'Alembert

1. Wave Equation

The first solution to the vibrating string problem.

$$ \frac{\partial^2 u}{\partial t^2} = c^2 \frac{\partial^2 u}{\partial x^2} $$

2. D'Alembert's Principle

Converting a dynamic problem into a static one by introducing inertial forces.

$$ \mathbf{F} - \frac{d\mathbf{p}}{dt} = 0 $$