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The programme shows how the interatomic force versus separation or interatomic potential energy versus separation curve can be established experimentally.
Metadata describing this Open University video programme
Module code and title: ST285, "Solids, liquids and gases"
Item code: ST285; 02
First transmission date: 17-02-1973
Published: 1973
Rights Statement:
Restrictions on use:
Duration: 00:23:48
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Producer: Andrew Millington
Contributors: Mike Pentz; Brian Smith; Alan Walton; Graham Weaver
Publisher: BBC Open University
Keyword(s): Atomic force curve; Atomic separations; Crystal whiskers; Equilibrium; Infinity; Linearity; Origin; Potential energy curve; Steel; Tensile tests
Footage description: The programme is introduced with a shot of the force/extension curve shown at the end of the previous programme (ST285/01). Pentz shows a simplified, enlarged version of this curve. He explains how a potential energy curve can be derived from a force/extension curve. Pentz places the potential energy curve below the force/extension curve on a graph. Using this graph, he introduces the concept of "binding energy". Alan Walton, with a graph showing an inverted force/extension curve. He discusses attractive and repulsive forces between atoms with the aid of the graph. Walton begins a discussion on how these forces can be determined quantitatively. Graham Weaver uses a tensile testing machine to apply force to a sample of steel. The force is monitored on a chart recorder. Weaver goes on to explain how the apparatus works. He then analyses the curve and shows that force is proportional to extension. Walton with a model of an array of atoms connected to one another by springs. He stretches the model by applying a force. Walton uses the model to explain how experiments on macroscopic samples can be used to obtain values for forces between single atoms. Graham Weaver stretches the steel sample further. The curve is again monitored but is no longer a straight line curve. Weaver uses a micrograph of a steel sample to explain why the force/extension curve is no longer a straight line. He goes on to explain why single crystals must be used in this experiment and tells how these are grown. Film shots of single crystals being grown. Film shots of a single crystal specimen being stretched to breaking point in a small tensile testing machine. Walton uses a force/extension graph to explain how parts of the force/extension curve were monitored. He then explains how information on the curve to the right of the peak is obtained. Walton with a simplified potential energy separation curve. He indicates the area which is to be measured. Walton also uses a diagram of an array of atoms to explain how measurements are made. Brian Smith with an apparatus which can grow samples of argon. He explains and shows how this is done. Smith measures the time and force required to evaporate a sample of argon. He writes his readings on a board. Walton calculates the bond dissociation energy from the readings taken by Smith.
Master spool number: 6HT/70369
Production number: 50521_1026
Videofinder number: 679
Available to public: no