Have you ever had a door that was more difficult to lock in the winter than in the summer? It may have seemed like a mysterious issue, but it turns out there's an actual scientific reason for it -- thermal expansion.

    In fact, all matter has a rate in which in which it expands and contracts when it is exposed to hot or cold temperatures. Use our thermal expansion calculator to see how a material will expand or contract using different temperature readings.

    But why does this happen? Read this guide to learn more!


    What is thermal expansion?

    Thermal expansion is the change in volume and area of a particular piece of matter in response to changes in temperature.

    In general, matter expands when exposed to hot temperatures and contracts when exposed to cold temperatures.

    Thermal expansion also has an effect on the density of matter.

    When matter is exposed to heat and expands, it then becomes less dense. The reverse is also true when matter is exposed to cold temperatures -- it increases in density.

    The manner in which matter expands depends on whether it is a solid, liquid, or gas.

    Thermal Expansion Of Solids

    Solids expand and contract in direct proportion to temperature change. Area expands twice as much as length, and volume expands three times as much as length.

    Materials like graphite and wood expand differently depending upon the direction in which they are expanding.

    Thermal Expansion Of Liquids

    Liquids, on the other hand, can only expand and contract in volume. One notable exception to thermal expansion, however, is water.

    Water expands when it is heated and when it freezes; frozen water is less dense than water in its liquid state.

    This is why ice on lakes and in oceans floats, and why lakes and oceans freeze from the top down.

    Thermal Expansion Of Gases

    Gas behaves less predictably, and it will expand as much as it can depending upon pressure.

    Co-Efficient Of Thermal Expansion

    The rate at which an object will expand and contract is dependent upon the type of material of which it is composed.

    This is referred to as the coefficient of thermal expansion. For example, wood will expand and contract more than metal when exposed to a particular temperature.

    Why does thermal expansion take place?

    Thermal expansion takes place because of kinetic energy. Kinetic energy is the energy of an object that it possesses due to its motion.

    Essentially a certain amount of kinetic energy is required to keep that object at its current speed, and that same level of energy will continue until that object changes speed.

    Temperature has an effect on the kinetic energy of the individual atoms within an object.

    An increase in temperatures causes an increase in the kinetic energy of the atoms. The atoms begin moving faster and pushing apart from nearby atoms and molecules, which ultimately makes that piece of matter larger.

    The reverse is true for matter that is exposed to cold temperatures. The cold causes the kinetic energy of the atoms within an object to slow down and contract.

    What are the formulas for thermal expansion?

    There are several different equations for thermal expansion. The proper equation is dependent upon the state of the matter that is expanding.


    For solids, use and linear expansion formula and an area expansion formula.


    For liquids, use a volume expansion formula.


    For gas, trying studying Boyle's Law, which examines how the pressure of a gas reacts to volume changes of the container in which it is held.

    Essentially, increases of volume equate to decreases in pressure, and decreases in volume result in increases of pressure.

    Alternatively, Charles's Law can be more directly applicable to thermal expansion as it describes how gases react to changes in temperature.

    How do you convert thermal expansion?

    When you want to convert thermal expansion, you're likely referring to the coefficient of thermal expansion.

    The coefficient of thermal expansion describes the how a material increases or decreases based on temperature. Or more formally, the degree of change in size per degree of temperature increase.

    The coefficient of thermal expansion can be calculated for each form of temperature measurement. The easiest way to do this is to use a thermal expansion converter, like the one on this page.

    What is thermal expansion of the ocean?

    Thermal expansion of the ocean is the rise in global sea levels as a result of rising global temperatures.

    Hotter water temperatures make for less dense oceans. Since liquids can only expand in volume, they cannot simply expand up or expand out.

    Thus, because expanding ocean waters need some place to go, they beg

    in to flow into previously exposed land areas, creating greater areas of ocean and reduced areas of land on Earth.

    Note that thermal expansion is not the sole reason for rising sea levels. Additional factors, such as melting ice sheets are also a major factor.

    What are some other examples of thermal expansion?


    Here's where the door mystery comes in. If you live in an area with dramatic fluctuations in temperature such as the midwestern or northeastern United States, you may notice that your front door has issues in both the winter and the summer.

    In the winter, cold air will cause your door and the door frame to contract. The portion of your deadbolt in the door frame will also contract, making it difficult to slide the actual deadbolt into the lock.

    In the summer, you likely won't have an issue with the deadbolt, but with the door itself. Warm weather will cause the door to expand and make it more difficult to fit within the door frame.


    Another example of thermal expansion in everyday life is the lid on a jar of jam or pickles.

    Have you heard of the trick to getting tight lids off jars? You run them under hot water, which will cause the lid to expand and make it easier to remove.

    The reason this trick works is that metal has a higher coefficient of thermal expansion relative to glass.

    This means that metal expands more than glass, thus the lid expands more than the jar, making it easier to remove.


    Old-fashioned thermometers contain mercury sealed in a glass tube called a capillary. Mercury has a much higher coefficient of thermal expansion than glass.

    The amount of mercury and the volume within the capillary have been calibrated so that the mercury rises in such a way that it reflects the temperature.

    Put more simply, the mercury in a thermometer expands when exposed to heat, and rises within the capillary to show the current temperature to which it is being exposed.

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