Which of the following is not a method of heat transfer?

Heat transfer can occur through various mechanisms: conduction, convection, and radiation are the three primary methods recognized in physics.

Conduction occurs when heat is transferred through direct contact between materials. This process relies on the collisions between particles; as one particle gains heat energy, it vibrates more and transfers energy to adjacent, cooler particles.

Convection is the transfer of heat through the movement of fluids (liquids and gases). Warmer, less dense fluid rises while cooler, denser fluid sinks, creating a circulation pattern that effectively transfers heat throughout the fluid.

Radiation is the transfer of heat in the form of electromagnetic waves. This method does not require a medium; heat can be transferred through a vacuum, such as how the sun warms the Earth.

Diffusion, on the other hand, describes the process where particles spread from areas of high concentration to areas of low concentration without the specific process of heat transfer in mind. While it involves the movement of particles, it does not specifically refer to heat transfer as defined by conduction, convection, or radiation. Therefore, diffusion is not a method of heat transfer, making it the correct choice in this context.