The direction of acceleration is consistent with the direction of external force. The positive and negative acceleration only represents the direction, not the magnitude. When the object is moving, if the acceleration is not zero, it is in the state of speed change. If the acceleration is greater than zero, it is acceleration, that is, the direction of acceleration and velocity is the same; If the acceleration is less than zero, it is deceleration, that is, the speed is opposite to the acceleration direction. The magnitude of acceleration is equal to the change of velocity in unit time; The direction of acceleration is always the same as the direction of velocity change. In particular, in linear motion, if
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