2. In mechanics, degree of freedom refers to the number of independent coordinates of a mechanical system. The degree of freedom of the system is zero, which means that the system cannot move, forming a geometrically invariant system with no redundant constraints. For example, if you cut grapefruit with a knife and cut it three times along the meridian of the North Pole, you will get six corners. These six angles can be regarded as three pairs, of which only two of the half three angles can be freely selected. Once the two values are determined, the third angle is only determined.