Joints

So far, we have talked about rigid bodies and colliders, but they were just single physical bodies. What about more complex mechanical systems? Imagine a rope that is holding a cage with a skeleton and a key inside. So, our protagonist decides to cut the rope to make the cage fall. Once the rope is broken, then the cage falls down. However, even before the rope is cut, the cage was under the effect of gravity. In fact, if our protagonist would have pushed the cage instead of cutting the rope, that would have started to oscillate. The reason is that the rope is giving a constraint to the cage — it is allowed to move only within a circle (or sphere if we are in 3D) that has per radius the length of the rope. Of course, when it oscillates, gravity makes the cage move on the border of this circle (or sphere). What if the rope were a rigid metal bar? Well, the cage would even have a harder constraint, because now it is forced to be only on the border of the circle (or sphere). And if the...