Which physical process is always accompanied by a heat exchange?

The correct answer pertains to weather phenomena, as these processes are intrinsically linked to the transfer of heat energy. Weather events like storms, rain, and wind are fundamentally driven by changes in temperature and pressure in the atmosphere. These changes often result from the warming of air by solar radiation, leading to convection currents and other meteorological processes.

In contrast, gravity is a fundamental force that does not inherently involve heat exchange; it acts on mass and does not directly affect thermal energy. Acceleration, while it can produce friction and heat in specific scenarios (like with mechanical systems), does not inherently involve heat exchange in its definition or as a fundamental characteristic. Similarly, magnetic fields are associated with the electromagnetic force and while they can have secondary effects on thermal processes, they do not always lead to heat exchange as a primary consequence. Thus, the link between temperature changes and heat exchange in weather phenomena makes it the most suitable choice for this question.