When an object is oscillating or vibrating in a wave motion , the speed of the object varies along the path. In this video, there are 3 examples of vibrating object. 1) Mass vibrating vertically from a spring 2) Pendulum bob oscillating 3) A particle vibrating up and down on a transverse wave In general, when the object is at the extreme ends of the oscillation or vibration , it is momentarily at rest . Hence its KE at these points is minimum or 0 J . And in the middle that is where the object is travelling the fastest , hence the KE is the maximum .