I just started my college prep math class on vectors. I had them read the book and then I talked about it and found a nice video on adding vectors graphically to show them. After the video, I sat with students to help them begin but they had trouble so today, I worked again and after three problems, I put the video on again and had the students watch it again. This time, I stopped the video at each step and we discussed how it related to what we were doing. This is working really well. Furthermore, I was asked to start the class again with the same video before they attempt additional problems.
In the past I would have shown one video and moved on but I think when it is a topic that is so different from any other mathematics they've had before, they need the reteaching and scaffolding and by reshowing the video numerous times. This seems to be working best with them.
I found an app that supposedly shows vector addition but it had no instructions and is not intuitive to use. Furthermore, it kept closing on me so that made it harder to use. I am going to continue to explore it and report back on it later.