Experiences

Hooke’s law. Indirect measurement of the elastic constant of a spring.

Gomboli Sandro

Italy

Vocational School

Physics

Laboratory

Direct

The physical vector, characterized by intensity, direction and orientation are a difficulty for the students when they begin to study the static.
The experience of Hooke's law applied on the elastic elongation of a spring allows you to understand the vector character of some physical strength as well as elongation of the spring.
Pupils also include the relationship between physical variables that can be represented by graphs. In this experience the track for the first time a graph expressing the elongation of the spring as a function of the applied force, verifying the direct proportionality.
The experiment consists in measuring – thanks to a measuring tape – the length of a spring to which five different masses are hung in the same configuration.
It will be possible to notice the direct proportionality between the weight and the stretching of the spring and, by measuring the elastic constant (its major feature) in an indirect way, its constant ratio.
In the end, thanks to a statistic analysis of random errors all through a short series of measurements, you can calculate the medium reading of the measurement of the elastic constant during the five tests and its approximate value.
The statistical analysis is fundamental because you deal with various aspects of Physics and of physical testing:
1) you can exemplify some general notions such as the definition of the material point (or particles) and rigid, elastic and plastic body.
2) for the first time you can focus on some vectors such as force and stretching and the basic notions of vector calculus concerning vectors having the same direction.
3) you can test the first cardinal equation of the Statics of the material point (or particles) in order to solve problems concerning Statics.
4) under an operational viewpoint you can apply the protocols according to the theory of measurement : statistical analysis of errors, a short series of measurements and the analysis of the propagation of the approximate values concerning indirect measurements.
5) for the first time it is possible to make a graph on a sheet of graph paper with all the necessary passages such as orientation, scales concerning the two axes, representation, data approximation and approximate values.
The different nature of the two forces, that of gravity (which is constant) and the elastic force of the spring (variable and depending on its position) are to be noticed.
For all these reasons this experiment takes some time, but it represents a fundamental passage for the comprehension of Physics, the first real approach to natural phenomena, their interpretation and their link with mathematical language.
This experiment is followed by a specially provided test, during which the formalism of the execution of procedures and necessary calculations needs to be observed.