👉 In physics, a "cross-arm" is a special type of physical object that exists in a closed system. This type of object has no internal structure or energy content but instead interacts with its surroundings through a mechanism called a "bridge," which allows it to move between two different states. For example, a crossarm could be a bridge made of materials that are both solid and hollow, like a steel tube. The material on top of the crossarm is more rigid than the material on the bottom
