MP Board · Class 9 · Science · MotionDefine acceleration. State its SI unit and explain what is meant by negative acceleration (retardation).

Acceleration is defined as the rate of change of velocity of an object with respect to time. Mathematically, it is expressed as: $$\text{Acceleration } (a) = \frac{\text{Final Velocity } (v) - \text{Initial Velocity } (u)}{\text{Time } (t)}$$ \nThe SI unit of acceleration is metre per second squared ($\text{m/s}^2$). \nAcceleration is taken as negative (also known as deceleration or retardation) when the velocity of an object decreases with time. This happens when the direction of acceleration is opposite to the direction of motion. For example, when brakes are applied to a moving vehicle, its velocity decreases, producing negative acceleration.