# Examples of Heat Expansion and Contraction

The expansion and contraction of a solid element can be produced by the action of heat (this is when the expansion of the element occurs) and by the action of cold (contraction).

When there is a sudden change in temperature (rise) most of the elements expand. When this temperature decreases, the elements contract. For example: On a very hot day, the wood expands but, when the temperature drops, it begins to generate noise as it contracts again.

However it is important to make a fundamental clarification: When solids expand as a result of heat, it does not mean that they increase in volume. What happens is that the distance between molecule and molecule increases causing the element to have an expansion. This expansion (or dilatation) exerts a considerable force.

This condition of solids is important to take into account, especially in bridge constructions, since it has been proven that a metal bridge that measures 50 meters and that goes from 0º C to 15º C in a short time can expand up to 12 centimeters.

However, not all solids expand in the same way and under 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 the degree of agitation of these increases.

In other words, what happens is that each particle begins “to vibrate “ and it is separated from the particle that it has next to it, in this way the expansion of the element takes place.

When the heat descends, the particles diminish the internal energy and little by little they are approached until being again one next to the other.

### Examples of heat expansion and contraction

1. When a bowl is placed in the refrigerator and removed. In order to remove the cold from the edge of the container, the same hermetic container must be immersed in hot water, in this way the plastic expands allowing the contents to be extracted from its interior.
2. Water. When heated (boiled) the molecules expand, when they cool down they contract and when they freeze, the water molecules compact.
3. Iron. This metal is found in nature in a solid state, that is, its molecules are closer to each other. However, due to the action of heat, this metal expands (expand) and iron becomes molten iron. The same is true of other metals such as aluminum, mercury, lead, etc.
4. Chewing gum. When chewing gum is at a high temperature, it melts. This is seen during a hot day. Then, if we put this gum in the refrigerator, it contracts and hardens.
5. The muscles of the body on a day with very low atmospheric temperatures. For this reason, some people have sore muscles after aerobic training 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.
6. Water carbonated in the freezer.
7. Timber. A very hot day it expands. Then, when the temperature drops, it begins to generate noise as it contracts again.
8. Railroad 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, it contracts again.
9. Glass. If we place a regular glass tumbler and add boiling water, the inside of the glass expands while the outside is cold. This causes the glass to break.
10. The thermometer. This is made up 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.