A bouncing ball has constant acceleration but changing velocity direction

Motion Along a Straight Line — AQA A-Level Physics

AccelerationThe rate of change of velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.. A vector quantity. Measured in m s⁻². due to gravity is constant and always directed downwards (ignoring air resistanceThe opposition to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). flow. The ratio of potential difference to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A).. Measured in ohms (Ω).).
At the highest point: displacementThe distance moved in a particular direction from a starting point. A vector quantity. Measured in metres (m). is maximum, velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹. is zero (momentarily at rest), velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹. changes from positive to negative.
At the lowest point (bounce): velocity changes instantaneously from negative to positive, but speed (magnitude) stays the same.
On a velocity-time graph, the ball produces a series of straight lines (constant $gradient = g)$ with sharp sign changes at each bounce.