Page 9 - 8-Sci-9 Sources And Effects Of Heat Energy
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9. SOURCES AND EFFECTS OF HEAT ENERGY  eLearn.Punjab

2. Fixing a Metal Tyre Over the Wheel

The metal tyres which are fixed over the wooden wheels of the carts are slightly smaller
than the wheels when they are cold. On heating, the metal tyre expands and its diameter
increases. Then hot tyre can easily be fitted onto the wheel. On cooling, the metal tyre
contracts and fits over the wheel tightly (Figure 9.10).

3. Fixing Axle into a Wheel

This method is mostly used to fit in the axle of train wheels. In this method, contraction is
used instead of thermal expansion. The diameter of the axle is slightly larger than the hub
of the metal wheel. The axle is placed in liquid nitrogen which is below -196 oC temperature.
The axle cools and contracts. It is then inserted into the hub of the wheel and is allowed
to come to room temperature. At room temperature, axle expands and fits into the wheel
tightly (Figure 9.11).

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