Acceleration

Acceleration is an important aspect of motion.  It describes how an object changes velocity over time, as it speeds up, slows down and changes direction.  Specifically, acceleration is defined as the change in velocity divided by time.  Velocity has distinctive shapes on motion graphs.  On a position-time graph, straight lines show constant or zero velocity and therefore zero acceleration.  Any curve represents non-zero acceleration, since a curve has a changing slope and the slope of a position-time graph is the velocity.  A change in velocity is acceleration.  When the position-time graph is any part of an upward-curving parabola, it represents a positive acceleration, and when the position-time graph is any part of a downward-curving parabola, it represents a negative acceleration.  The slope of a velocity-time graph shows the acceleration, since rise over run is change in velocity over time.  A positive slope means a positive acceleration, a negative slope shows a negative acceleration and a zero slope shows a zero acceleration and a constant velocity.

For more information on velocity and acceleration view the video clip Velocity and Acceleration in One Dimension from Discovery Education™ streaming.