press B to add an object
press alt to switch between box and bubble
use the mouse wheel to change the size
press E to add an elastic link
press R to add a rigid link
press U to add an elastic link with the last object
press T to add a rigid link with the last object
press O to add a rope
press M to add a motionless object
press space to stop time
hold D and click to delete an object
click and drag an object to move it
press C to clear the scene