Question

For an oscillating Pendulum would the acceleration be constant or changing?
I had to do a lab for my Physics Class and we used a motion detector to show kinematics graphs of a pendulum. The velocity vs. time graphs was sinusoidal. Wouldn't that meant that the acceleration is changing because the slope of the graphs is going from positive to negative constantly, or would the acceleration just be gravity which is 9.8 m/s^2