The expansion and contraction of a solid element can be produced by the action of heat (this is when the element expands) and by the action of cold (contraction).
When there is a sudden change in temperature (increase) most of the elements expand. When said temperature decreases, the elements contract. For example: on a very hot day the wood expands but, as the temperature drops, it begins to generate noise as it contracts again.
However it is important to make a fundamental clarification: When solids expand due to heat, it does not mean that they increase their volume. What happens is that the distance between molecule and molecule increases causing the element to have an expansion. This expansion (or dilation) exerts considerable force.
This condition of solids is important to take into account, especially in bridge constructionssince it has been verified that a metal bridge that measures 50 meters and that goes from 0º C to 15º C in a short time can dilate up to 12 centimeters.
However, not all solids expand in the same way and at the same temperature. For example, aluminum expands 2 times more than iron metal.
What happens inside the solid?
By increasing the temperaturewhat happens is that the internal energy of the particles increases and their degree of agitation rises.
In other words what happens is that each particle begins “to vibrate” and it is separated from the particle next to it, in this way the expansion of the element is produced.
When the heat decreases, the particles decrease their internal energy and little by little they get closer until they find themselves next to each other again.
Examples of expansion and contraction of heat
- When a bowl is placed inside the refrigerator and taken out. In order to remove the cold from the edge of the container, the same hermetic container must be submerged in hot water, in this way the plastic expands, allowing the content to be extracted from its interior.
- Water. When heated (boiled) the molecules expand, when cooled they contract and when frozen, the water molecules compact.
- Iron. This metal is found in nature in a solid state, that is to say that its molecules are closer together. However, due to the action of heat, this metal expands (expands) and iron becomes molten iron. The same happens with other metals such as aluminum, mercury, lead, etc.
- Chewing gum. When chewing gum is at a high temperature, it melts. This is seen during a hot day. Then, if we put this chewing gum in the refrigerator, it shrinks and hardens.
- The muscles of the body on a day with very low atmospheric temperatures. For this reason, some people get sore muscles after an aerobic workout or on very hot days and then very cold. Who regulates this is the liquid (water) of our body. But the pain intensifies if the body is dehydrated.
- Water carbonated in the freezer.
- Timber. A very hot day it expands. Then, when the temperature drops, it begins to generate noise as it contracts again.
- Rails of the train tracks. These are built with a certain distance being slightly separated. Tar is then placed in this space to allow the metal to expand on very hot days and then, as the temperature drops, to contract again.
- Glass. If we put a glass of ordinary glass and add boiling water, the internal part of the glass expands while the external part is cold. This causes the glass to break.
- The thermometer. This is composed of liquid mercury. As in liquid elements the particles are relatively distant from each other, mercury, when exposed to heat (for example, body fever), the mercury rises up the thermometer since it has become more liquid.
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