Todays video is by Maria, Teo and Yehya (I think). They chose to explain why a block slides as the angle of a slope is increased. To do this they needed to show the components of force acting down the slope. This is problematic since algodoo shows horizontal and vertical components only. Actually what Algodoo shows is components parallel and perpendicular to gravity so instead of changing the angle of the slope the angle of gravity is varied, this wouldn't look right so the orientation of the simulation is fixed on a rectangular object pivoted at one end. This acts as a plumb line. I had to add springs to this to provide damping or the whole view would oscillate.

Here is the video: I have no idea whose voice that is. I hadn't realised I had a robot in the class.