I created this simulation for use later this semester with my IP4 classes, to illustrate the concept of phase difference between two oscillating particles.
https://ejss.s3-ap-southeast-1.amazonaws.com/phasedifference_Simulation.xhtml
Update (26 August 2020): I have also created a GeoGebra app to demonstrate the same principle.
Fantastic. Helped me visualize phase difference problems.