Timeline of heat engine technology
In engineering and thermodynamics , a heat engine performs the conversion of heat energy to mechanical work by exploiting the temperature gradient between a hot "source" and a cold "sink" . 
<triplet> thermodynamics <subj> heat <obj> studies <subj> energy <obj> studies <subj> temperature <obj> studies <triplet> heat <subj> thermodynamics <obj> studied by <subj> energy <obj> subclass of <triplet> mechanical work <subj> heat <obj> opposite of <subj> energy <obj> subclass of