What type of heat source is characterized as mechanical?

The correct answer is compression, as it refers to a type of mechanical heat source. Compression involves the process of mechanically compressing a gas, which increases its pressure and temperature. This phenomenon is particularly noteworthy in systems such as refrigeration or air conditioning, where gases are compressed to produce a heating effect or cool an environment.

In the context of heat sources, other options represent different forms of heat transfer or generation. Electrical heat relies on electric currents to produce thermal energy, radiant heat is associated with electromagnetic waves transferring energy, and convection heat involves the transfer of heat through fluid movement. While these methods all generate or transfer heat, they do not inherently involve mechanical processes like compression does. Understanding how compression leads to heat generation helps clarify its unique classification among heat sources.