TENSION AND COMPRESSION Tension and compression can be applied to a rod or wire with a resultant change in length called delta L. This delta L will be produced when a force is applied on top of the rod or wire in order to stretch it or compress it. As it turns out, the change in length is proportional to its original length and the force applied. It is inversely proportional to the cross-sectional area of the rod or wire. This makes sense because a lesser cross-sectional area and a greater original length will make it easier to have compression or tension affect the length of the rod or wire. There is also a constant called the Young’s modulus or the elastic modulus, which is dependent on the substance. Things with a large Young’s modulus will have a large tensile stiffness because they deform less for a given tension or compression. The units for this constant are 109 Newtons per meter squared. You should also know the definitions for stress and strain. Stress is the ratio of force to the surface area of the object, while strain is the ratio of the change in length or delta-L and the total length or L. When you use the equation for tension and compression, you get stress equaling the Young’s modulus multiplied by the strain. These equations are listed in figure 21:
Figure 21.
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