Two common ways of expressing a changing speed are:
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Acceleration: This refers to the rate of change of velocity over time. It can be expressed in units such as meters per second squared (m/s²) and indicates how quickly an object speeds up, slows down, or changes direction.
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Velocity: Often expressed as a vector quantity, velocity includes both speed and direction. Changes in velocity indicate changes in speed (how fast something is moving) and/or direction (where it is going). Changes in speed can be expressed in terms of increases or decreases in velocity.
These two concepts are foundational in the study of motion in physics.