Have you ever noticed that railway tracks have small gaps between them? Or why do electric wires sag in summer but tighten in winter? These happen because of thermal expansion—the property of matter to expand…
Thermal Expansion: Why Objects Change Size
Ever noticed that railway tracks have small gaps between them? Or why do electric wires sag in summer but tighten in winter? These happen because of thermal expansion—the property of matter to expand when heated and contract when cooled. In this article, we’ll learn about thermal expansion in solids, liquids, and gases with simple examples. Thermal expansion occurs because particles in a substance move more and occupy more space as the temperature increases. Therefore, this movement causes the material to expand. When you heat a metal rod, its particles vibrate more vigorously and push each other apart, increasing its length.
What is Thermal Expansion?
An object expands when heat makes its particles vibrate more and occupy more space. When cooled, the particles slow down, and the object contracts. This effect is called thermal expansion.
Types of Thermal Expansion
1. Linear Expansion (Increase in Length)
Heating a solid increases its length while keeping its width and thickness nearly constant. We call this linear expansion, which occurs because of thermal expansion.
Formula:
The change in length (∆L) is calculated by:
∆L = α L₀ ∆T
- α = Coefficient of linear expansion (different for each material)
- L₀ = Original length
- ∆T = Change in temperature
Examples:
- Railway tracks have small gaps to allow expansion in summer.
- Metal bridges expand on hot days, so they are built with expansion joints.
- Concrete roads have grooves to prevent cracking due to expansion.
Why does this happen?
Heating makes atoms vibrate more, pushing them slightly apart, increasing their length.
2. Areal Expansion (Increase in Area)
Heating a flat object like a metal sheet expands its surface area through thermal expansion, a phenomenon we call areal expansion.
Formula:
The change in area (∆A) is given by:
∆A = β A₀ ∆T
- β (≈ 2α) = Coefficient of areal expansion
- A₀ = Original area
- ∆T = Change in temperature
Examples:
- Metal plates used in construction expand in summer.
- Pipes with large surfaces bulge slightly when heated.
- Bimetallic strips (used in thermostats) bend because two metals expand differently.
Why does this happen?
Since expansion happens in all directions, the area increases more noticeably than length alone.
3. Volume Expansion (Increase in Volume)
Heating liquids and gases expands them in all three dimensions—length, width, and height. Thus, this volume expansion results from thermal expansion.
Formula:
The change in volume (∆V) is calculated by:
∆V = γ V₀ ∆T
- γ (≈ 3α) = Coefficient of volume expansion
- V₀ = Original volume
- ∆T = Change in temperature
Examples:
- Liquids in thermometers rise when heated (e.g., mercury or alcohol).
- Hot air balloons expand when heated, making them float.
- Fuel tanks are not filled completely to allow for expansion.
Why does this happen?
In liquids and gases, particles move freely, so heating makes them spread out in all directions.
Comparison of Expansion in Solids, Liquids, and Gases due to thermal expansion
| Property | Solids | Liquids | Gases |
|---|---|---|---|
| Expansion | Least | Moderate | Highest |
| Particle Movement | Vibrate in place | Slide past each other | Move freely |
| Example | Metal rod | Mercury in thermometer | Air in balloon |
Examples of Thermal Expansion in Daily Life
✅ Railway Tracks: Gaps are left between tracks to allow expansion in summer. If these gaps were not present, the tracks could buckle due to the heat, leading to potential accidents.
✅ Electric Wires: Wires loosen in summer (expand) and tighten in winter (contract).
✅ Bimetallic Strips: Used in thermostats because metals expand differently. When the temperature changes, the two metals in a bimetallic strip expand at different rates, causing the strip to bend.
✅ Hot Air Balloons: Air expands when heated, making the balloon rise. As the air inside the balloon is heated, it becomes less dense than the cooler air outside. Therefore, this difference in density causes the balloon to lift off the ground and float.
FAQ’s
Q1. Why do bridges have expansion joints?
Ans: To prevent damage from thermal expansion in summer and contraction in winter.
Q2. Why does a glass bottle crack when hot liquid is poured suddenly?
Ans: The inner part expands due to heat, but the outer part remains cool, causing uneven stress and cracking.
Q3. Which expands more: solids, liquids, or gases?
Ans: Gases > Liquids > Solids (Gases expand the most because their particles are far apart.)
Q4. What is the coefficient of thermal expansion?
Ans: It measures how much a material expands per degree temperature change.
Thermal expansion is an important concept in physics and engineering. Hence, engineers design structures like bridges, pipelines, and railway tracks with gaps. Understanding this helps in building safer and more efficient machines and infrastructure.
Reference
- Yakout, M., Elbestawi, M. A., & Veldhuis, S. C. (2018). A study of thermal expansion coefficients and microstructure during selective laser melting of Invar 36 and stainless steel 316L. Additive Manufacturing, 24, 446-456. https://doi.org/10.1016/j.addma.2018.09.035
- Kaladze, T. D., & Misra, A. P. (2023). Thermal expansion of atmosphere and stability of vertically stratified fluids. Physics Letters. A, 480(128990), 128990.
https://doi.org/10.48550/arXiv.2306.04372
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Shreya Satsangi is a passionate Master’s student studying Quantum Technologies at UIMP (Universidad Internacional Menéndez Pelayo), Spain. She has an impressive academic background, holding an undergraduate degree in Physics (Honours) from Dayalbagh Educational Institution, Agra, where she achieved the highest grade in her degree, earning the prestigious Director’s Medal. This recognition is a testament to her strong foundation in physics and her dedication to excellence.
Her interest in the dynamic and fascinating field of quantum science has been a driving force throughout her academic journey. Shreya is particularly captivated by the intersections of quantum physics, quantum computing, and quantum sensing, and is eager to explore the potential of these cutting-edge technologies. She has a deep commitment to understanding how quantum mechanics can be harnessed to revolutionize computing, communication, and sensing, and is excited about the vast implications of quantum research for the future.
Beyond her academic pursuits, Shreya has actively contributed to the scientific community, both in India and internationally. She has worked with organizations such as QuantumGrad, Girls in Quantum, and BeyondResearch, where she has gained valuable hands-on experience and expanded her knowledge of quantum technologies. Through these platforms, she has been involved in organizing various quantum science sessions, aimed at fostering greater understanding and interest in the field of quantum science.
Shreya’s passion for science extends into science communication, where she strives to inspire the next generation of scientists and thinkers. She is an avid writer, having authored numerous blogs on Quantum Technologies on Medium. In her writing, Shreya seeks to simplify complex quantum concepts, making them accessible and engaging for a broader audience. In addition to quantum technologies, she has also written articles on other areas of physics, including electronics and fluid mechanics, further showcasing her versatile interests and ability to communicate complex topics effectively.
Shreya believes in the importance of outreach and engagement in science and works tirelessly to encourage young minds to think scientifically and embrace curiosity. Her work in science communication is driven by her desire to make science more relatable and to inspire others to pursue careers in physics and quantum technologies. She sees science as not just a discipline but a way of thinking, and she is committed to sharing that mindset with others.
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With her solid academic background, hands-on experience, and dedication to science communication, Shreya is poised to make a significant impact in the world of quantum technologies. She is eager to continue exploring the frontiers of quantum research and contributing to the development of new technologies that have the potential to reshape the future.
