Force

In the study of statics we are concerned with two fundamental quantities: length or distance, which requires no explanation, and force. The quantity length can be seen with the eye but with force, the only thing that is ever seen is its effect. We can see a spring being stretched or a rubber ball being squashed but what is seen is only the effect of a force being applied and not the force itself. With a rigid body there is no distortion due to the force and in statics it does not move either. Hence, there is no visual indication of forces being applied.

We detect a force being applied to our human body by our sense of touch or feel. Again, it is not the force itself but its effect which is felt – we feel the movement of our stomachs when we go over a humpback bridge in a fast car; we feel that the soles of our feet are squashed slightly when we stand.

We have now encountered one of the fundamental conceptual difficulties in the study of mechanics. Force cannot be seen or measured directly but must always be imagined. Generally the existence of some force requires little imagination but to imagine all the different forces which exist in a given situation may not be too easy. Furthermore, in order to perform any analysis, the forces must be defined precisely in mathematical terms.