The time rate of change of velocity. Acceleration is a vector quantity. For one-dimensional motion, the axis, the zero, and the positive direction are prespecified. A positive acceleration indicates motion in prespecified direction, while a negative acceleration indicates the opposite direction. An acceleration that points in the direction opposite of the velocity is sometimes called a deceleration.
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Representations
Differential
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Graphical
Besides explicit acceleration graphs, acceleration can be found from the slope of a velocity vs. time graph or from the curvature (concavity) of a position vs. time graph.
Through Motion Diagrams
In a motion diagram, the acceleration can be estimated by looking at the spacing of the individual snapshots (assuming that the snapshots are separated by equal time intervals). If the spacing is increasing with time, the acceleration is in the direction of motion. If the spacing is decreasing with time, the acceleration is opposite to the direction of motion.