If it moves it can break! That is a basic principle of engineering. Moving parts are vulnerable to forces applied to any of the non-fixed parts. Folding knives have a hinge; they are made of several parts: the blade, the handle, the locking mechanism and probably some type of release switch and/or lock. A fixed bladed knife is one piece of steel with a gripping surface attached.

Although my Ph.D. is not in physics, I am a certified science teacher and study physics as part of my job instructing Pramek Adaptive Combatives, which is very science based. I teach knife defense and also knife combatives as part of the curriculum as a Pramek Adaptive Combatives Instructor and have also taught knife defense and knife combatives at several seminars in the past. I usually receive opposition to the fact that I do not teach the usage of folders as combat knives.

Whenever an object has two parts connected by a hinge breakage can occur as well as a serious injury to the person holding the knife if the hinge does break. The knife user will have his or her fingers cut quite severely.

The torque is the product of the magnitude of the perpendicular force multiplied by the lever arm. Because you are applying a force to the end of the folding knife’s blade, there will be a push back of force (Newton’s 3rd Law – equal and opposite reaction) and that force can ultimately be manifested in a perpendicular load on the blade and subsequently create a substantial magnitude of torque at the pivot point (hinge).