In part, the significance of this work comes from bridging two varieties of research. The first variety of research is work on intuitive physics knowledge. Given that we, as humans, must function in the physical world, it is manifestly evident that we must know a great deal about the behavior of that world. When we let go of an object over a trash bin, we know what is going to happen—the object will fall down until it strikes the bottom of the bin, or any other trash that is already there. If we tip over a glass full of water, we are aware that the water will begin to spill out, if we pass a certain critical angle. We may know that if we rub a balloon on a wool sweater, the balloon will, temporally, stick to a wall. All of this informally gained knowledge of the physical world is intuitive physics knowledge.