Fade editing

 We had to present our ideas in class today and one of the other teams asked sir how to execute a fade seen that they had planed for one of their scenes 

Sir taught us that in order to show something disappear we need to shoot two videos one with the subject and the other without it, overlay it and change the opacities, however the camera must be very stable and nothing except for the subject that has to disappear/fade should be moved