Mechanical energy is energy applied to something via work. For example, the pressure added to the compressed gas thanks to mechanical energy can now be used to transfer that energy by doing work elsewhere (perhaps by pressurizing an actuator to turn a valve). read more
Thus, the work is the transfer of energy. Let us take a closer look at the concept. Whenever work is done upon an object, a force is applied on to it and the object is displaced because of this force. read more
(From wikipedia on Work) Now heat: heat is energy transferred from one body or thermodynamic system to another due to thermal contact when the systems are at different temperatures. It is also often described as the process of transfer of energy between physical entities. read more