ELASTICITY, STRESS, AND STRAIN We have covered things like friction and drag forces that affect the motion of an object. The topic now at hand are those things that affect an object’s shape. Deformation involves a change in an object’s shape because of the application of a force. Small deformations will “spring back” to the original shape—more so in certain situations where the object has some elasticity. The size of the deformation will be proportional to the force so that for small deformations, there is Hooke’s law that is obeyed. So, what is Hooke’s law? In equation form, Hooke’s law states that force equals a proportionality constant multiplied by the change in deformation. The proportionality constant depends on the shape and nature of the object as well as the direction of the force. What it means is that the deformation of an object is proportional to the force. Things like bones do not deform much and will break when a force is applied to them. This brings up the topic of tensile strength, which is the breaking stress that will result in breakage or fracture of the material. Figure 20 graphs deformation and describes Hooke’s law and tensile strength.
Figure 20.
52