¶ Twelve Universal Degrees of Freedom
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Index Entry
Here are some drawings I made to show the different degrees of freedom for a mast. if I wanted to have a mast on the face of the Earth it would take me a minimum of three legs, and a tension member to hold these legs down: so it takes four members. I can have one compression member and three tension members or three compression members and one tension. It always comes out four. I can put the hole in the ground and we will find that there is still the four. We will find that we might have to have the mast bending over like that, and it would take two tension members going up to hold it: that is called a gin pole; and then it takes a fourth member of gravity to pull this end down so there are four members operating. You could do that with two compression legs, sometimes called a jack in the Navy, and one tension member and gravity: four members every time. So there are the four degrees of freedom and the local twist you will remember which gave us twelve.1 began to see then that we would always have these kinds of fournesses always operative.
