decelerates

Decelerates is the third-person singular present tense form of the verb decelerate, meaning to slow down or cause something to slow down. The word derives from de- (reverse) and celerare (to speed), reflecting a reduction in speed rather than a change in direction alone.

In physics, deceleration refers to a reduction in the magnitude of velocity. Technically, velocity is a vector quantity, and deceleration describes the situation in which the component of acceleration along the velocity direction is opposite to the motion. This results in a decreasing speed, even if the object changes direction as part of the motion. If an object’s speed increases while moving in the same direction, it is not decelerating, though it may be accelerating in the opposite sense.

Common usage of decelerates appears in everyday language to describe braking or slowing down. For example, a car decelerates when the driver applies the brakes, or a planet decelerates as it climbs out of a gravitational well. In engineering and physics, deceleration is often quantified as a negative acceleration or as the rate of decrease of speed over time.

Decelerates can also appear in grammatical contexts, where it denotes an action performed by a subject. In both everyday and scientific language, the term emphasizes a reduction in speed rather than a mere change in direction.

See also: acceleration, velocity, deceleration, braking, kinematics.