A hovercraft is a machine, and all machines require energy input to make them work. The term used to describe the study of energy is thermodynamics.

Thermodynamics is a field that deals with energy, heat, work, entropy, and spontaneity. It is described by four laws: The Laws of Thermodynamics.

The Zeroth Law of Thermodynamics: For three bodies in a system, if body A is in thermal equilibrium with body B and body B is in thermal equilibrium with body C, then body A is in thermal equilibrium with body C. This means that all three bodies are at the same temperature and provide a system in which temperatures can be compared to a standard via a thermometer). The unusual naming of this law as “The Zeroth”, where most sets of laws begin with “The First”, stems from the fact that this law was formulated well after the other three, but is often considered to be a more fundamental law than the others. It was not unknown to the early thermodynamicists, but was considered a basic truism not worth the distinction of being a “Law”.

The First Law of Thermodynamics: The total amount of energy in a closed system does not change, regardless of transformations the various forms of energy in the system may undergo. This law is often stated as: ΔQ = ΔU + ΔW, where ΔQ is the heat transferred from the environment to the system, U is the internal energy of the system, and W is the work done by the system. The First Law of Thermodynamics is what is often referred to as the Law of Conservation of Energy.

The Second Law of Thermodynamics: This law states that any time something in the Universe changes, the total amount of entropy, or disorder, stays the same or increases. When, as happens in energy conversions in the world, energy is converted to heat, that heat energy is in the form of random motion in the particles that constitute the system. This random motion cannot be converted back into useful energy without the addition of more energy from an outside source, which in turn undergoes an increase in entropy greater than the decrease in entropy of the first system. This is how life in the Universe works — life is an inherently ordered system based on the conversion of energy. e First Law of Thermodynamics things take energy from food, sunlight, or thermal energy, and use that energy to continually combat entropy in their localized systems. The effect of this is to remove useful energy from and increase the entropy in the environment. It should be emphasized that the total energy in the universe is not decreasing, it is merely changing from a form that can be used to a form that cannot be used. The Second Law of Thermodynamics also deals with the efficiency of engines. In this form, it states that an engine cannot convert all of the heat energy put into it to work — some of it has to be passed out as heat. Similarly, it is impossible to make a refrigerator that simply removes heat from a cooler system to a warmer one. Instead, work must be added to get heat to flow from a lower to a higher temperature. This aspect of the Second Law is why combustion engines do not spontaneously (without external cause) cool, but instead require cooling systems.

The Third Law of Thermodynamics: A system at absolute zero, the temperature where all motion in particles stops, has an entropy that is a clearly defined constant. (Strictly speaking, quantum mechanics states that there is still some motion at absolute zero, which is the state from which no more energy can theoretically be extracted), has an entropy that is a clearly defined constant. Another statement of this law is that a system cannot be brought to a temperature of absolute zero in a finite number of steps.

The three original laws of thermodynamics are sometimes stated more concisely (if less informatively) as:

1. You can't win.
2. You can't break even.
3. You can't get out of the game

Quiz Question:

1. In a system a piston moves by the expansion of burning fuel. If 24 MJ [1.77×10⁷ ft-lb] of energy is supplied by the burning fuel and the work done by the piston is 15 MJ [1.11×10⁷ ft-lb], determine the change in internal energy of the fuel.