Question

A three legged stool will not rock, even if the legs are of differnt lengths. Many four legged stools wobble. Explain

Answer 1

Because it is like a plane. In order to have a plane, there must be at least 3 points. In a chair with three legs, the legs are all in the same plane. 

Answer 2

a four leg stool would not always wobble on an uneven floor. thinking the stool legs are even the four leg stool wobble because one leg will not  tough the floor