Actually this question can be answered from various perspectives. According to physics, both of stiffness and rigidity are a lot different from each other. From daily usage point of view, Rigid 1. An iron rod is Rigid Stiff 1. My muscles have become stiff after an unusually long exercise. 2. The door hinge has become stiff. May be we should think of applying some grease. I think you can make out the difference from the above examples. Rigid is something, that is not bendable under normal circumstances. And stiff is usually used for temporary states. Also, you can use "rigid" for describing the mentality of a person. For instance, "He has got a rigid mentality.

Very similar. Rigid can mean either stiff (will not bend) or fixed in place (will not move). . The rod was rigid enough to hold up the flower pot. The staff was stiff enough to hold up the flower pot. . Rigid can mean the structure. The rod coming out of the ground was rigid enough to hold the flower pot. = It will not fall over. Stiff means more that it will not bend. . A person who is rigid is someone who has rules & does not break them, or expects you to not break them. A person who is a bit stiff may not be be comfortable in groups.