Motion Detector Lab

Today in MM's core we did the motion detector stations. I do not think that you can have positive velocity with no acceleration because you need acceleration to have velocity, right? If a person is walking away from the detector the graphs would both be jagged and would be rising. I think the graphs were messy, especially the one where we tried to make it as straight as possible , were due to human error because when people walk their bodies go up and down. But I am afraid that this was inevitable.