👉 In physics, a perturbation is an alteration or change in the state of a system due to external forces acting on it. These changes can be positive (increasing) or negative (decreasing), and they can occur at any time during the motion of the system. For example, consider a simple pendulum: the pendulum bob will oscillate with different speeds and directions depending on the force applied to it by an external agent such as a spring. The speed and direction of the oscillation