Two identical weights are suspended by identical threads with the same kind of thread tied to their bottoms. When you pull downward on the bottom thread, which one of the threads will break? It depends on how you pull. If you pull very quickly, the bottom thread will break due to the inertia of the mass of the weight. If you pull uniformly downward, the top thread always breaks because the weight increase the tension in the top thread.
|2 ring stands||021-2A|
|metal rod||above 021-23|
|threads with looped ends||Ring stands in SW 017|