Coefficient of linear expansion - you can calculate everything

Everyone, for sure, is familiar with the tapping of the wagon wheels. Or the sound of the tram wheels. Everyone knows that the reason for this is the gap at the junction between the rails. And for what it is made? The answer is simple - to compensate for the expansion of the rails when heated. It is also a well-known fact that when heated, the bodies expand, and when compressed, they contract. A measure of this expansion or contraction is the coefficient of linear expansion.

The molecular theory of the expansion of a body upon heating is explained by the increase in the velocity of motion of atoms and molecules of matter. As a result, in the crystal lattice the amplitude of oscillations of atoms increases and, as a consequence, the linear dimensions of the body increase. And how much the increase will occur can be determined using a formula in which the coefficient of linear expansion is applied.

Now we need to explain the physical meaning of the coefficient. It shows how much the body length will increase by 1 ° C when heated. This value is insignificant and has its own for each material. Thus, the coefficient of linear expansion of the steel is 0.000011 per 1 ° C. What a really similar value is, you can understand by a simple example. If the Earth is wrapped around the Earth with an iron wire, the length of which is 40,000 km, then with a temperature increase of 1 ° C, the length of the wire will increase by 400 meters.

The coefficient of linear expansion is extremely important for any engineer. It allows you to take into account the change in body size at a temperature drop. So, if during a year the temperature in the city changes from plus fifty degrees Celsius to minus fifty degrees Celsius, this will cause significant changes in the length of the same rails. If they are solid, the result will be their bending. Here to avoid this phenomenon, and make a gap between the rails when they are laid.

For different materials, the value of the coefficient will be different. For steel, its value has already been given, and the coefficient of linear expansion of aluminum is 0.0000024 per 1 ° C.

However, the above arguments and examples suffer a certain one-sidedness. When we talk about increasing the size of the body when heated, not only length increases, but also other dimensions - width and height. The increase in size will lead to an increase in volume, and then one can speak of a volumetric expansion of bodies. True, such a concept is more likely to apply not to solids, but to liquids.

A simple experiment, which will confirm this, can do each independently. Put a kettle on the fire, filled with water to the very top. When the water warms up, it will increase in volume and "run away" from the kettle. But there is a positive use of this effect. Everyone is familiar with liquid thermometers - that street, that medical. They are also built on the effect of increasing the volume when heated.

In technology, sometimes ignoring this increase leads to sad consequences. To compensate for the increase, special measures must be used. Many had to see a long row of pipes (pipeline) laid along the surface. And suddenly on an equal place the pipes form a huge zigzag. This is not a simple zigzag, its magnitude is strictly defined, while the coefficient of linear expansion was used in the calculation. A similar zigzag was made to compensate for the linear increase in the dimensions of the pipes.

You can also give many examples of the use of linear and volumetric extensions in the technique, but the above examples are sufficient to understand the essence of the phenomenon. Of course, the anomalous behavior of some substances, the same water, is very curious. At it at freezing the volume does not decrease, but increases. This will be another factor that confirms the unique properties of water.

So, in this article, based on the simplest and most vivid examples of life, such a concept as linear expansion of bodies and the coefficient of linear expansion is defined. Examples of the use of the extension in engineering and in everyday life are given, and the concepts of the order of magnitude of the coefficient mentioned are given.