July 31, 2025

Naz Keskin

11th Grade

Yahya Akel Science High School

Every moment, we exist in a vivid mosaic of different energy that pulses through the world around us. It is the invisible force that connects everything. Have you ever considered how this dynamic energy influences our lives, shaping not just our physical surroundings but also our thoughts, emotions, and actions? Let’s dive deeper into the pervasive nature of energy and explore how it manifests in our everyday experiences through the lens of thermodynamics.

In thermodynamics, there are two important terms: systems and surroundings. Systems are the main beings or environments we focus on, and surroundings are what is left. Together, they make up the universe. There are, in total, three types of systems in the universe. The first system is an open system.

As humans, we are living proof of an “open” system. We receive chemical energy in the form of food and sunlight, and we transfer and use our energy through movement like walking, running, swimming, etc. We exchange both matter and energy with our environment. All these exchanges are little to no different from the exchanges between hot and cold objects, gas molecules, or anything else you might find in a physics textbook. 

The second type of system is called a closed system. It is when the system can only exchange energy, not matter, with other systems. And lastly, we have the isolated system, which refers to when the system cannot exchange either energy or matter. A perfectly isolated system is hard to come by, but an insulated drink cooler with a lid is conceptually similar to a true isolated system. The items inside can exchange energy with each other, which is why the drinks get cold and the ice melts a little, but they exchange very little energy (heat) with the outside environment.

There are four thermodynamic laws that shape the world we live in. The first law of thermodynamics is that energy cannot be created or destroyed. Alternatively, we can call it the conservation of energy. Ultimately, the First Law of Thermodynamics is a statement that energy can be transferred between the system and the surroundings by transferring heat (q) or by the performance of mechanical work (w).

ΔE = q + w

Energy is not created or destroyed; it only transfers between systems and their surroundings. When the system gains energy, the surroundings lose an equivalent amount, and vice versa. If we were to give a couple of examples, we could say when light bulbs transform electrical energy into light energy or when one pool ball hits another, transferring kinetic energy and making the second ball move.

The second law of thermodynamics states that energy can be converted into different forms, which can be categorized as more useful or less useful. It turns out, in every real-world energy transfer or transformation, some amount of energy is converted to a form that’s unusable (unavailable to do work). In most cases, this unusable energy takes the form of heat. While heat can perform work under certain conditions, it cannot be completely converted into other forms of energy that do work with 100% efficiency. Therefore, every time energy is transferred, some amount of useful energy becomes less useful or is lost.

You might be asking: If heat does not work, what does it do? The heat that does not do work goes directly towards increasing the disorder of the universe. When two objects, such as two blocks of the same metal, exist at different temperatures, the system exhibits a level of organization: the molecules are categorized by their speeds, with those in the cooler object moving slowly and those in the hotter object moving quickly. When heat flows from the hotter object to the cooler one—an occurrence that happens spontaneously—the molecules in the hot object begin to slow down while those in the cool object speed up. This process continues until the molecules reach a uniform average speed. Consequently, instead of having a distinct separation between fast and slow molecules, we end up with a single, more homogeneous pool of molecules all moving at a similar speed, resulting in a less ordered state than we initially had.

This degree of randomness within a system is referred to as entropy. It is now understood that with every energy transfer, a portion of energy is transformed into what is known as “unusable” forms, such as heat. Since heat, which does not perform work, contributes to increasing the randomness of the universe, we can articulate a biology-relevant interpretation of the Second Law of Thermodynamics: every energy transfer that occurs will elevate the entropy of the universe and diminish the amount of usable energy available for doing work (or, in some extreme instances, leave the overall entropy unchanged).

The third law of thermodynamics states that the entropy of a system at absolute zero is constant, or it is impossible for a process to bring the entropy of a given system to zero in a finite number of operations. At very low temperatures, particles become highly ordered, but some energy remains. This law is important in fields like cryogenics and superconductivity, as it helps explain the unique properties of materials near absolute zero. It highlights the limits of thermodynamic processes and the relationship between temperature and disorder.

The zeroth law of thermodynamics establishes the concept of thermal equilibrium, which serves as the foundation for defining temperature. It states that if two systems are each in thermal equilibrium with a third system, then they are also in thermal equilibrium with one another. But what exactly does thermal equilibrium mean? It refers to a state where two physical systems are in contact and there is no net transfer of thermal energy between them, indicating that both objects are at the same temperature. The zeroth law employs this principle of thermal equilibrium to determine how two distinct systems can be recognized as having the same temperature. For instance, when molten rock emerges from a volcano, it releases heat to the surrounding atmosphere until both the rock and the air reach the same temperature. Despite the significant differences between the two systems, thermal equilibrium provides a common definition of temperature for both.

Thermodynamics reveals the critical role of energy in shaping both our physical world and our daily experiences. The laws of thermodynamics underscore that energy is conserved and transformed, often leading to increased entropy. This understanding encourages us to recognize the dynamic exchanges of energy happening around us, highlighting the intricate balance that governs our universe.