# What does it mean to say that an object undergoes a deceleration? Can this term be used without ambiguity?

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Deceleration refers to a situation where the rate of change of the velocity is negative. If the velocity of an object at time `t_0` is `V_0` and the velocity at time `t_0 + h` is `v_1` , and it is decelerating, the value of `v_1` is less than that of `v_0` .

If an object is decelerating `(v_1 - v_0)/(t_0 + h - t_0) < 0`

The term can be used without ambiguity.

Deceleration means that an object's velocity decreases at an increasing rate, or (perhaps more clearly) **when an object's acceleration is less than 0**. You might think of it as negative acceleration.

For Example:

An object with an acceleration of -3cm/sec^2 would be decelerating.

An object with velocities (measured at every second): 100 mph, 90 mph, 70 mph, 40 mph, 0 mph is also decelerating.