Deceleration

Deceleration is the process of reducing velocity. In physics, it is a form of acceleration—the rate of change of velocity with respect to time. Acceleration is a vector quantity; its sign depends on the chosen direction. When an object's speed decreases in a given direction, its acceleration is opposite in direction to its velocity and is described as negative acceleration or deceleration. Conversely, if velocity and acceleration share the same direction, the speed increases.

Measurement and calculation: a = dv/dt, instantaneous deceleration is the instantaneous rate of change of velocity. Average deceleration over a time interval is Δv/Δt, where Δv is the change in velocity (often negative if slowing). Magnitude of deceleration is typically given as a positive value to denote how quickly motion slows, regardless of direction.

Examples and contexts: Common sources include friction between surfaces, air drag, and braking systems in vehicles. Gravity can produce deceleration in upward or forward motion; for an object thrown upward, gravity causes its speed to decrease until it reverses downward.

Applications: stopping distance depends on initial velocity and deceleration: d = v0^2/(2a) for constant deceleration a (positive quantity). Real-world deceleration varies with speed, mass, surface, and resistance.

Deceleration is a common concept in physics and engineering, essential for understanding motion, safety, and energy losses.