(a) Describe three ways in which you could increase the internal energy of an open system. (b) Which of these methods could you use to increase the internal energy of a closed system? (c) Which, if any, of these methods could you use to increase the internal energy of an isolated system?

Internal energy refers to the total energy contained within a system, encompassing both the kinetic energy of particles moving and vibrating and the potential energy resulting from the forces between these particles. A core principle of thermodynamics is that internal energy can be altered through various interactions with its surroundings. For instance, heating a gas increases the speed of its particles, which in turn elevates the system's internal energy. To visualize this, imagine a pot of water on a stove; as the water heats up, the increased motion of the water molecules contributes to a rise in the water's internal energy. Similarly, compressing a gas within a piston does work on the system, thereby increasing its internal energy.

An open system is one that freely exchanges both energy and matter with its environment. A boiling kettle, for example, loses water to the surrounding air as steam and absorbs heat from the stove burner. Increasing the internal energy of an open system could involve adding heat, performing work on the system, or introducing mass with higher energy into the system. The concept plays a vital role in understanding various physical, biological, and chemical processes where exchange with the surroundings is essential for the system's function.

Contrary to an open system, a closed system allows for the transfer of energy in the form of heat or work, but not mass. An example of this could be a sealed, inflated balloon — it can absorb heat from its environment or have work done on it when squeezed, but no air (mass) can enter or leave. This understanding is crucial when considering systems where maintaining a constant mass is necessary for accurate analysis or for specific operational requirements, such as in refrigeration systems or hydraulic pistons.

An isolated system is the 'fortress' of thermodynamic systems, where neither energy nor matter can pass through its boundaries. A perfect example, although theoretical, would be an insulated flask that perfectly retains heat and contains a vacuum around its contents, preventing any heat transfer or matter exchange. This concept is helpful when exploring theoretical predictions in thermodynamics since it provides a simplified environment free from external influences.

Heat transfer is the process by which thermal energy is exchanged between physical systems, depending on the temperature difference between them. The most familiar forms of heat transfer include conduction, convection, and radiation. In the context of increasing internal energy, when a system absorbs heat (think of a metal rod becoming hot at one end when heated at the other), the energy of the particles within the system increases. This concept is paramount in disciplines such as meteorology, engineering, and environmental science, where heat exchange is a fundamental phenomenon.

The term 'work done on system' in thermodynamics often involves forces causing displacement within a system, which in turn increases the system's internal energy. An everyday example would be pumping air into a bicycle tire. The work done by the pump on the air inside the tire increases the air's internal energy and, subsequently, the tire's pressure. It's a crucial concept in understanding how energy transformations can be harnessed, controlled, and utilized in mechanical systems and engines.