Final answer:
The reference provided does not directly answer the question about stacking bags, but it suggests activities related to physics principles of vector addition and mass. Stacking bags by 'stepping back and cross keying' is likely associated with stability, similar to how vectors can illustrate balance and direction.
Step-by-step explanation:
When stacking bags of material that are the same width, the instruction 'step back and cross key the bags' refers to a method for stabilizing the stack. This might involve alternating the direction the bags are laid so that each bag is supported by the two underneath it in a crisscross fashion, enhancing the overall stability of the stack. However, the materials provided in the reference are about adding vectors in a physical sense and crumpling paper to demonstrate mass, which are activities related to physics principles.
The 'adding vectors' activity with the masking tape is designed to teach students how to visualize and understand vector addition, direction, and magnitude in a tangible way. By walking steps and labeling them, students are essentially creating a physical representation of vectors. In the context of stacking materials, one can think of each bag as a vector with both magnitude (weight, size) and direction (the orientation in which the bag is placed).
The crumpling paper activity seems to be an exploration of mass and could be relevant to engineering, where understanding the properties of materials and how mass is distributed is essential for construction and stacking objects effectively.