Many general physics laboratories involve the use of springs to demonstrate Hooke's law, and much ado is made about how this can be used as a model for describing the elastic characteristics of materials at the molecular or atomic level. In recent years, the proliferation of computers, and appropriate sensors, have made it possible to demonstrate this on a small scale without the necessity of purchasing or fabricating specialized equipment. This paper describes an experiment that uses these new resources to determine the elongation of a very fine wire as a function of stretching force. A graphical presentation clearly demonstrates the range of validity of Hooke's law and also allows one to see the onset of plastic deformation without catastrophic failure of the wire. The experiment is easy to perform with off-the-shelf equipment and may be readily incorporated into a standard Hooke's law laboratory exercise.

1.
R.H. Bacon, The Lloyd William Taylor Manual, Advanced Undergraduate Experiments in Physics, edited by T. B. Brown (Addison-Wesley, Reading, MA, 1961), pp. 35–37.
2.
A.
Niculescu
and
R.
Shumaker
, “
Apparatus for measuring Young's modulus
,”
Phys. Teach.
41
,
364
367
(Sept.
2003
).
3.
T. B.
Greenslade
Jr. and
R.
Wilcox
, “
An inexpensive Young's modulus apparatus
,”
Phys. Teach.
31
,
116
117
(Feb.
1993
).
4.
PASCO scientific, Roseville, CA, Part: Rotary Motion Sensor, Model CI-6625; http://www.pasco.com.
5.
Vernier Software and Technology, Beaverton, OR, Part: LabPro and Logger Pro 3; http://www.vernier.com.
6.
EasyPlot™, Stuart Karon, Spiral Software, Norwich VT; http://www.spiralsoftware.com/ep/eplot.html.
7.
McMaster Carr, Atlanta, GA, Part: 8455A16; http://www.mcmaster.com.
8.
Note: A couple of experimental runs were performed with the support wire wrapped several turns around the large support rod and held with transparent tape. However, the authors suggest using the pin vise because it is less problematic.
9.
Note: With this restriction, ignoring the circumference of the loop around the shaft introduces little error to the initial length yo. If more than one loop around the shaft is used, the loop circumference may become significant in determining y0.
10.
National Physical Laboratory (NPL, the UK's National Measurement Laboratory); http://www.npl.co.uk/pressure/faqs/altgrav.html.
11.
Note: The general method described in this paper has been applied to wires of other materials in our general physics laboratories with similar results.
12.
Note: 5-, 10-, 20-, and 50-g masses were mined from standard mass sets using a calibrated Metler analytical balance with a resolution of 0.01 g.
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