The first law of thermodynamics states that the change in internal energy of a system equals the net heat transfer into the system minus the network is done by the system.
Delta U - the change in internal energy U of the system.
Q - the net heat transferred into the system, that is, Q is the sum of all heat transfer into and out of the system.
W - the work done on or by the system.
An example of energy in motion is the boiling kettle. The water in the boiling kettle turns into vapour because the heat is delivered from the stove to the kettle. The entire system gets hotter, the Work is done, namely the evaporation of the water and up to the whistling of a kettle.