In a system where two bodies are at equal temperatures and in thermal equilibrium, there is indeed no net heat loss between them. This is because heat naturally flows from a region of higher temperature to a region of lower temperature until thermal equilibrium is reached.
However, even though there is no net heat loss, the two bodies can still exchange energy through other means, such as conduction, convection, or radiation.
Conduction: If the two bodies are in physical contact, they can transfer energy through conduction. Conduction occurs when heat is transferred through direct contact between particles. The particles with higher energy (higher temperature) transfer some of their energy to the particles with lower energy (lower temperature) until thermal equilibrium is established.
Convection: Convection involves the transfer of heat through the movement of a fluid. If the two bodies are in contact with a fluid medium, such as air or water, the fluid can carry heat energy between the bodies. This happens through the circulation of the fluid, where warmer fluid moves away from one body, and cooler fluid replaces it, establishing a heat exchange.
Radiation: All objects emit thermal radiation based on their temperature. Even when two bodies are not physically touching or in a fluid medium, they can still exchange energy through thermal radiation. Thermal radiation is the emission of electromagnetic waves due to the temperature of an object. Objects at the same temperature can still emit and absorb radiation from each other, enabling energy exchange.
It's important to note that in a system in thermal equilibrium, while energy may be exchanged through these mechanisms, the net heat transfer between the two bodies is zero since they are at the same temperature. This means that the energy gained by one body through conduction, convection, or radiation is balanced by an equal amount of energy lost by the other body, resulting in no net heat loss or gain between them.