Question

Many people have tried to make a perpetual motion machine, but none have been successful although some have claimed success. Use the law of conservation of energy to explain why such a device is impossible.

Short answer

A perpetual motion machine is impossible as it violates the law of conservation of energy.

Step-by-step solution

Understanding Perpetual Motion

A perpetual motion machine is designed to operate indefinitely without an external energy source. It aims to generate more energy than it consumes, essentially running forever.

Law of Conservation of Energy

The law of conservation of energy states that energy cannot be created or destroyed in an isolated system. The total energy in a closed system remains constant over time.

Application of the Energy Law

Given the conservation of energy law, a machine cannot produce more energy than it consumes, as the energy output must always be equal to or less than the energy input in a closed system.

Explaining the Impossibility

Since energy cannot be created, a perpetual motion machine, which requires energy to be generated continuously without an input, violates the conservation of energy law, making it impossible.

Key concepts

Law of Conservation of Energy

The law of conservation of energy is a fundamental principle in physics. It states that the total energy in an isolated system remains constant over time. This means that energy within the system can change forms, like turning potential energy into kinetic energy, but it can't be created or destroyed. For instance, when you swing on a playground swing, at the highest point, your energy is mostly potential. As you move down, this converts into kinetic energy, and back to potential as you rise again. The total energy stays the same, illustrating the conservation process. This principle underpins why certain machines, like perpetual motion devices, are practically impossible. A machine claiming to generate energy indefinitely without an external source clashes with this law, as it implies energy creation from nothing, which doesn't align with energy conservation.

Closed System

A closed system in physics is one where no matter enters or leaves, and no energy is allowed to be added or removed from outside the system. This type of system is crucial to understanding the limits of energy transfer and conversion, especially when discussing the impossibilities of perpetual motion machines. In a closed system, all the energy is contained within, meaning the energy processes within must adhere strictly to the conservation of energy.
In practical terms, think of a closed container where all heating and cooling occur internally without external influences. If a system were to produce more energy than it consumes, it would need some external input or leak energy, violating the definition of a closed system. This concept helps to confirm that in any real-world scenario, sustaining a machine like a perpetual motion device without external energy input is not feasible.

Energy Output

Energy output refers to the amount of energy produced by a system, device, or process. In the context of machines, energy output must always balance with, or be less than, the energy input in a closed system. For a perpetual motion machine, the goal would be to create energy continuously, exceeding any input without stopping.
However, this defies the basic rules of thermodynamics and energy conservation. Imagine a car trying to run without fuel – it needs an energy source to provide output, whether it’s gasoline or electricity. Similarly, any machine's energy output cannot exceed the energy input. Even the most efficient engines or systems have energy losses, often in the form of heat, which is why there's never perfect energy conversion.
Energy output is limited by these losses, making the idea of an eternally running machine an intriguing, yet practically impossible concept under the current laws of physics.