Cecily Zamora
The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created or destroyed, but can only be transferred from one form to another. This means that the total energy of a system remains constant, even if it is converted from one form to another. For example, kinetic energy is converted to heat energy when a driver applies the brakes to slow down a moving car. While the first law of thermodynamics has been precisely supported and never violated in properly conducted experiments, it is so general that its predictions cannot all be directly tested.
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What You'll Learn
Energy cannot be created or destroyed
The first law of thermodynamics is based on the law of conservation of energy, which states that energy cannot be created or destroyed in a closed system, but can only be transferred from one form to another. This principle is so fundamental to our understanding of the universe that it is considered one of the most basic principles of physics.
The first law of thermodynamics is a general principle that applies to all thermodynamic processes and systems. It states that the total energy of a system remains constant, even if it is converted from one form to another. This means that the amount of energy in the universe has always been and will always be the same. The law distinguishes two principal forms of energy transfer: heat and thermodynamic work. Heat is the transfer of thermal energy due to a temperature difference, while work is the transfer of energy that occurs when a force is applied over a distance.
For example, when you take a bath, you are transferring energy from the hot water to your body, warming it up. Similarly, when you press the brakes on a car to slow down, the kinetic energy of the car is converted into heat energy due to the friction between the brakes and the wheels. In both cases, energy is conserved and is neither created nor destroyed, but simply transformed from one form to another.
The first law of thermodynamics also applies to biological processes such as photosynthesis, where plants absorb solar energy and convert it into chemical energy, and human metabolism, where the food we eat is converted into energy to power our bodies. In addition, it is related to the concept of internal energy, which is the energy stored within a system due to the activity of its particles.
While the first law of thermodynamics has never been violated in properly conducted experiments, it is important to note that it is a general principle that may not apply in extreme or unique circumstances.
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Energy can be transferred or transformed
The first law of thermodynamics is based on the law of conservation of energy, which states that energy cannot be created or destroyed. However, it can be transferred or transformed from one form to another. This principle is summed up by the equation:
Total energy at the start of a process = Total energy at the end of a process
This means that the total energy within a system remains constant even if it is converted from one form to another. For example, when a driver applies the brakes to slow down a moving car, the kinetic energy of the car is converted into heat energy.
Energy transfer is the movement of energy from one location to another. For example, thermal energy radiates from the Sun, heating both the land and ocean. The wind generated from this process possesses kinetic energy, which it can then transfer to grains of sand on a beach by carrying them a short distance. If the moving sand hits an obstacle, friction is created, and its kinetic energy is transformed into thermal energy, or heat.
Energy transformation is the changing of energy from one type to another. For instance, lightning converts electrical energy into light, heat, and sound energy. A more mundane example is an electric fan, which transforms electrical energy into kinetic energy.
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Work and heat are interrelated
The first law of thermodynamics is based on the law of conservation of energy, which states that energy cannot be created or destroyed, but can be transferred from one form to another. This law distinguishes two principal forms of energy transfer: heat and thermodynamic work.
Work and heat are indeed interrelated. Heat is a form of energy, and energy is the capacity to do work. For example, a heat engine in a car is ready to do work because it contains a certain amount of stored energy. When work is done, energy is transferred between systems or from one form of energy to another. So, heat energy is what the engine contains, and work is what is done with that heat energy. It is either lost to the surroundings or converted to kinetic energy.
Work is motion against an opposing force. For instance, raising a weight against the opposing force of gravity requires work. The magnitude of the work depends on the mass of the object, the strength of the gravitational pull on it, and the height through which it is raised. Work is the primary foundation of thermodynamics and, in particular, the first law. Any system has the capacity to do work. For example, a compressed or extended spring can be used to bring about the raising of a weight.
The first explicit statement of the first law of thermodynamics, by Rudolf Clausius in 1850, referred to cyclic thermodynamic processes and the existence of a function of state of the system, the internal energy. The first law of thermodynamics allows for many possible states of a system to exist. However, experience indicates that only certain states occur. This eventually leads to the second law of thermodynamics and the definition of another state variable called entropy.
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Internal energy changes
The first law of thermodynamics is based on the law of conservation of energy, which states that energy cannot be created or destroyed, only transformed from one form to another. This law is particularly concerned with the transfer of energy as heat and work. Work, in the context of thermodynamics, refers to motion against an opposing force, such as raising a weight against the force of gravity.
Internal energy is a state variable that refers to all the energy within a given system, including the kinetic energy of molecules and the energy stored in chemical bonds. The internal energy of a system increases when heat is added to it or when work is done on it. Conversely, the internal energy of a system decreases if the system gives off heat or does work.
For example, when a driver presses the brakes in a car to slow down, the kinetic energy of the car is converted into heat energy. In this scenario, the internal energy of the car system increases due to the addition of heat energy, which raises the temperature of the brakes.
The first law of thermodynamics can be mathematically represented as:
ΔU = Q - W
Where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system.
It's important to note that internal energy is not directly measurable in systems more complex than an ideal gas. Instead, changes in internal energy are inferred by monitoring changes in the temperature of the system.
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Perpetual motion machines are impossible
The first law of thermodynamics is based on the law of conservation of energy, which states that energy cannot be created or destroyed, only transformed from one form to another. For example, kinetic energy is converted to heat energy when a driver brakes to slow down a car.
Perpetual motion is the motion of bodies that continue forever in an unperturbed system. A perpetual motion machine is a hypothetical machine that can do work indefinitely without an external energy source. However, these machines are impossible as their existence would violate the first and/or second laws of thermodynamics. The second law of thermodynamics states that an isolated system will move toward a state of disorder, and the more energy is transformed, the more is wasted.
A perpetual motion machine would have to produce work without energy input, which is not possible. Machines that extract energy from finite sources cannot operate indefinitely because they are driven by the energy stored in the source, which will eventually be exhausted. For example, devices powered by ocean currents will eventually run down as their energy source, the Sun, will burn out.
Despite this, many have attempted to create perpetual motion machines, dating back to the Middle Ages. Modern designers and proponents often use other terms, such as "over unity", to describe their inventions. However, the inviolability of the laws of physics has not stopped people from trying to break them. According to Simanek's online museum, the first documented perpetual motion machine was a wheel created by Indian author Bhaskara in the 12th century. Other attempts include a 16th-century windmill, 17th-century siphons, and several water mills.
In summary, perpetual motion machines are impossible as they would violate the fundamental laws of thermodynamics and physics.
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Frequently asked questions
The first law of thermodynamics is a formulation of the law of conservation of energy in the context of thermodynamic processes. It states that energy can be converted from one form to another, but it cannot be created or destroyed.
No, the first law of thermodynamics cannot be broken. It is a fundamental principle of the universe and has never been violated in any properly conducted experiments. It is so reliably established that it is used to test the accuracy of experiments.
The first law of thermodynamics states that the total energy of a system remains constant, even if it is converted from one form to another. This means that the internal energy of a system will change depending on the work interaction that takes place across its boundaries. If work is done on the system, the internal energy increases, and if work is done by the system, the internal energy decreases.
Sure, a common example is a heat engine. When you apply the brakes in a car, the kinetic energy of the moving car is converted into heat energy, which slows the car down. The total energy remains the same, but it has been converted from one form to another.
