Again, I had discussion about “weightless” with an AT teacher in Facebook.
An AT teacher says “To be weightless then means to somehow be free of this downwards-acting force.” Then the teacher says “both of the weightlessness boxes – a net zero equilibrium force, and no preferential strains” as conditions of weightless. It will not be “free of downwards-acting force”, though either conditions(boxes) are fulfilled.
Zero net force acting an object doesn’t mean “free of downwards-acting force” on the object. The object is just receiving another same amount of force from opposite direction. The object is still receiving downwards-acting force, which is gravity force. So, it is not free of downwards-acting force.
The teacher says that an object is weightless if both stress and strain are evenly distributed throughout its structure, (which is “no preferential strains” in the teacher’s word). This is nothing to do with “free of downwards-acting force”. This is just the pattern of distribution of stress and strain. Again, the forces (stress and strain) are still there, even though these are distributed evenly. They won’t go away.
There are logical leap in his reasoning. Therefore, his original idea(proposition) that a tensegrity structure is weightless and independent of gravity (free of downwards-acting force) is not convincing (it will be not true). By the way, human structure is not tensegrity in definition, and so humans are not weightless and independent of gravity. Nor is an anglepoise lamp.
The teacher’s resultant application to his use or teaching use based on his idea will not work well because his idea will not be true. It will be something like “we will feel weightless because we are weightless.” We still feel our weight, no matter how fully we apply the AT. I think that it is really important to feel and evaluate our weight for our better use. This will be a core skill in my opinion. I keep testing this in my lessons, and it works well.
I know that some AT teachers using the concept of tensegrity in order to explain the primary control, i.e., why the AT works. I know that a tensegrity structure has unique and different feature compared with ordinary structures we see in daily environment, so it is a bit mysterious. The AT is also unique and different from other method, and the AT has not been well explained using science terms. So, the AT is also a bit mysterious. Tensegrity and the AT has common charactersitics such as unique, different and mysterious, but this doesn’t mean the AT can be well explained with tensegrity concept. This will have logical leap. It is difficult to explain the reason why the AT works, but it has to be logical and reasonable. If it is not, it will be religious.