Work (thermodynamics)
In this experiment, the friction and agitation of the paddle-wheel on the body of water caused heat to be generated which, in turn, increased the temperature of water.  Both the temperature change ∆T of the water and the height of the fall ∆h of the weight mg were recorded.  Using these values, Joule was able to determine the mechanical equivalent of heat. Joule estimated a mechanical equivalent of heat to be 819 ft•lbf/Btu (4.41 J/cal).  The modern day definitions of heat, work, temperature, and energy all have connection to this experiment.