Hook’s Law. This was enunciated by Robert Hooke in the 17th Century. It deals with the deformation of solid materials due to unbalanced external forces, such as stretching and compression. The images show that a spring can either compressed or stretched. In both cases the length of the spring changes. The difference between the original length of the spring and the changed length will give the change in length. According to hooke’s law this change is directly proportional to the applied force. The graph shows how the extension of a spring has changed according to the change of pulling force. The straight line graph up to about 7.5 N shows that the extension or stretch is directly proportional to the applied force. Beyond that the spring does not obey the Hook’s Spring Constant
F = k x x The constant k is called the SPRING CONSTANT This is true only up to the elastic limit. We can re write the formula as k = F / x Here although we calculated in milimeters normally the unit given is newton per meter. . Elastic Potential EnergyIf a spring having a spring constant of 0.5 showed an extension of 3 cm what is the elastic energy stored in the spring? Energy is equivalent to work done. W = Force x extension.(x) F = k x extension.(x) As the force starts from zero the average force becomes F /2. W = ½ kx2 . Potential energy = ½ kx2
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4.1 The real length of the spring. 4.2 The elastic limit. 4.3 The spring constant.
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