The term “acceleration” is used in physics to describe a change in the velocity of an object, and it is a vector quantity, which means that it indicates both magnitude and direction.
Something that is traveling with positive velocity, velocity is also a vector, and experiencing negative acceleration is slower. In contrast to this, an object that has negative acceleration as well as negative velocity is actually moving faster.
It is often easier for someone to understand acceleration in general, and negative acceleration in particular, by first understanding velocity. Although the terms “speed” and “acceleration” are sometimes used synonymously in common conversation, these three words have very different meanings in reference to physics.
“Speed” is a measure of the distance an object travels in a given period of time, and is often expressed in miles per hour (mph) or meters per second (m / s).
Acceleration ”is similar to velocity, but it indicates not only the actual velocity itself but also the direction an object is moving, which makes it a vector quantity. This means that an object traveling at a speed of 20 m / s and another traveling at -20 m / s are both moving at the same speed but in opposite directions.
“Acceleration” is a measure relative to the change in speed of an object, and is often expressed in terms of meters per second, per second (m / som / s2). An object that moves at rest one second, then moves at 10 m / s the next second, 20 m / s the next, and 30 m / s the next second has an acceleration of 10 m / s2 since this is the speed change.
One of the simplest ways for a person to see negative acceleration is by throwing something into the air. When the thrown object leaves your hand, it moves at a certain speed, for example 40 m / s.
The force of gravity pulls down on the object as it travels upward in the positive direction, giving it an acceleration of about -10 m / s2. After one second the object continues to move at 30 m / s, another second later and is moving at 20 m / s, and after two more seconds it stops briefly before continuing to accelerate downward.
Negative acceleration simply indicates the direction of the acceleration, and it can mean that an object is increasing or decreasing in speed.
An object that is moving with a positive velocity, that has a negative acceleration, is slowing down. On the other hand, an object that is moving with negative acceleration, and with negative velocity, is actually moving faster.
This same basic principle also holds for positive acceleration; when the direction of velocity and acceleration are equal, the object is moving faster, and when they are opposite, the object is decelerating.