Describe an experiment that illustrates the modern concept of heat as a form of energy and how work can be converted into heat.

(N/A) In the modern concept,the caloric theory (the idea of heat as a fluid) was discarded.
An important experiment in this connection was performed by Benjamin Thomson (Count Rumford) in $1798$.
He observed that the boring of a brass cannon generated a significant amount of heat.
More significantly,he noted that the amount of heat produced depended on the mechanical work done,rather than the sharpness of the drill.
In the caloric theory,a sharper drill would have been expected to scoop out more 'caloric' fluid from the pores of the metal,but this was not observed.
The explanation for these observations is that heat is a form of energy,and the experiment demonstrated the conversion of energy from one form to another,specifically from mechanical work to heat.