Variable Acceleration

When a = f(t), we integrate: v(t) = v₀ + ∫a(t') dt', x(t) = x₀ + ∫v(t') dt'.

Common cases: a = kt gives parabolic v(t); a = sin(ωt) gives oscillatory v.

Numerical integration (Euler, Runge–Kutta) is used when no closed form exists.