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Why does the substance expand on heating? | Physics in Depth

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According to the postulates of Kinetic theory of gases, all matter is composed of atoms and molecules. When the substance is heated, the size of atoms/molecules remains unchanged but their space changes. As we increase the heat, the particles(atoms/molecules) vibrate more rapidly and takes up more space.  That is, more vibration is induced as we increase the heat increasing the average distance between the particles that results in expansion. We should remember that the size of the particles does not increase but the space between them does.
To put it in a nut shell, the expansion is caused due to the vigorous vibration of the atoms/molecules induced by the application of heat.

Image source mansfieldct

In this figure, we can see that the workers are trying to reconnect two wheels that have been separated due to the extreme cold. The oil-soaked rope is burnt next to the track which will cause the track to expand and thus reconnect.

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