Hi all! I am hoping your combined brains can help me with a problem in analyzing a technical rope rescue system I have been using for a few years. Here is the scenario:
There is a patient on one end of a rope. This rope runs up and over a pulley and back down to the ground where a rescuer is located (next to the patient). The rescuer tethers themselves to the patient; this creates a loop from the patient up to the pulley, down to the rescuer, and over to the patient. The rescuer then climbs the rope. As they climb the loop gets smaller and pulls both the patient and the rescuer up. (For this analysis assume no friction, a massless rope, and everything is occurring in free space.)
The system has a theoretical mechanical advantage of 2:1 where the load is both the patient and the rescuer. All of this is agreed upon in the rescue community. However, what is disagreed upon is if this should be classified as a counterbalance, or a haul system.
The rational for saying it is a counterbalance is that one mass (person) balances out the other (in part). So there must be some counterbalance going on. The opposite argument is that since both the patient and the rescuer are part of a single load, it is just a haul system. In other words, it can not be a counterbalance if the single load is holding itself up.
Personally I think the system is dynamic and can't be treated like there is one load. So I think there is a counterbalance at work, however, I would like clarity of thought and sound arguments to sway me because I'm literally hanging my life off this system! Any and all help would be greatly appreciated!
There is a patient on one end of a rope. This rope runs up and over a pulley and back down to the ground where a rescuer is located (next to the patient). The rescuer tethers themselves to the patient; this creates a loop from the patient up to the pulley, down to the rescuer, and over to the patient. The rescuer then climbs the rope. As they climb the loop gets smaller and pulls both the patient and the rescuer up. (For this analysis assume no friction, a massless rope, and everything is occurring in free space.)
The system has a theoretical mechanical advantage of 2:1 where the load is both the patient and the rescuer. All of this is agreed upon in the rescue community. However, what is disagreed upon is if this should be classified as a counterbalance, or a haul system.
The rational for saying it is a counterbalance is that one mass (person) balances out the other (in part). So there must be some counterbalance going on. The opposite argument is that since both the patient and the rescuer are part of a single load, it is just a haul system. In other words, it can not be a counterbalance if the single load is holding itself up.
Personally I think the system is dynamic and can't be treated like there is one load. So I think there is a counterbalance at work, however, I would like clarity of thought and sound arguments to sway me because I'm literally hanging my life off this system! Any and all help would be greatly appreciated!